the same,and they search for certain information in particular places.If these structural expectations are continually violated,readers are forced to divert energy from understanding the content of a passage to unraveling its structure.As the complexity of the context increases moderately,the possibility of misinterpretation or noninterpretation increases dramatically. We present here some results of applying this methodology to research reports in the scientific literature. We have taken several passages from research articles (either published or accepted for publication)and have suggested ways of rewriting them by applying principles derived from the study of reader expectations.We have not sought to transform the passages into "plain English"for the use of the general public;we have neither decreased the jargon nor diluted the science.We have striven not for simplification but for clarification. Reader Expectations for the Structure of Prose Here is our first example of scientific prose,in its original form: The smallest of the URF's(URFA6L),a 207-nucleotide (nt)reading frame overlapping out of phase the NH,-terminal portion of the adenosinetriphosphatase(ATPase)subunit 6 gene has been identified as the animal equivalent of the recently discovered yeast H-ATPase subunit 8 gene. The functional significance of the other URF's has been,on the contrary,elusive.Recently, however,immunoprecipitation experiments with antibodies to purified,rotenone-sensitive NADH-ubiquinone oxido-reductase [hereafter referred to as respiratory chain NADH dehydrogenase or complex I]from bovine heart,as well as enzyme fractionation studies,have indicated that six human URF's(that is,URF1,URF2,URF3,URF4,URF4L,and URF5, hereafter referred to as ND1,ND2,ND3,ND4,ND4L,and ND5)encode subunits of complex I. This is a large complex that also contains many subunits synthesized in the cytoplasm. [*The full paragraph includes one more sentence:"Support for such functional identification of the URF products has come from the finding that the purified rotenone-sensitive NADH dehydrogenase from Neurospora crassa contains several subunits synthesized within the mitochondria,and from the observation that the stopper mutant of Neurospora crassa,whose mtDNA lacks two genes homologous to URF2 and URF3,has no functional complex I."We have omitted this sentence both because the passage is long enough as is and because it raises no additional structural issues.] Ask any ten people why this paragraph is hard to read,and nine are sure to mention the technical vocabulary;several will also suggest that it requires specialized background knowledge.Those problems turn out to be only a small part of the difficulty.Here is the passage again,with the difficult words temporarily lifted: The smallest of the URF's,and [A],has been identified as a [B]subunit 8 gene.The functional significance of the other URF's has been,on the contrary,elusive.Recently,however,[C] experiments,as well as [D]studies,have indicated that six human URF's [1-6]encode subunits of Complex I.This is a large complex that also contains many subunits synthesized in the cytoplasm. It may now be easier to survive the journey through the prose,but the passage is still difficult.Any number of questions present themselves:What has the first sentence of the passage to do with the last sentence?Does the third sentence contradict what we have been told in the second sentence?Is the functional significance of URF's still "elusive"?Will this passage lead us to further discussion aboutthe same, and they search for certain information in particular places. If these structural expectations are continually violated, readers are forced to divert energy from understanding the content of a passage to unraveling its structure. As the complexity of the context increases moderately, the possibility of misinterpretation or noninterpretation increases dramatically. We present here some results of applying this methodology to research reports in the scientific literature. We have taken several passages from research articles (either published or accepted for publication) and have suggested ways of rewriting them by applying principles derived from the study of reader expectations. We have not sought to transform the passages into "plain English" for the use of the general public; we have neither decreased the jargon nor diluted the science. We have striven not for simplification but for clarification. Reader Expectations for the Structure of Prose Here is our first example of scientific prose, in its original form: The smallest of the URF’s (URFA6L), a 207-nucleotide (nt) reading frame overlapping out of phase the NH2 -terminal portion of the adenosinetriphosphatase (ATPase) subunit 6 gene has been identified as the animal equivalent of the recently discovered yeast H+ -ATPase subunit 8 gene. The functional significance of the other URF’s has been, on the contrary, elusive. Recently, however, immunoprecipitation experiments with antibodies to purified, rotenone-sensitive NADH-ubiquinone oxido-reductase [hereafter referred to as respiratory chain NADH dehydrogenase or complex I] from bovine heart, as well as enzyme fractionation studies, have indicated that six human URF’s (that is, URF1, URF2, URF3, URF4, URF4L, and URF5, hereafter referred to as ND1, ND2, ND3, ND4, ND4L, and ND5) encode subunits of complex I. This is a large complex that also contains many subunits synthesized in the cytoplasm.* [*The full paragraph includes one more sentence: "Support for such functional identification of the URF products has come from the finding that the purified rotenone-sensitive NADH dehydrogenase from Neurospora crassa contains several subunits synthesized within the mitochondria, and from the observation that the stopper mutant of Neurospora crassa, whose mtDNA lacks two genes homologous to URF2 and URF3, has no functional complex I." We have omitted this sentence both because the passage is long enough as is and because it raises no additional structural issues.] Ask any ten people why this paragraph is hard to read, and nine are sure to mention the technical vocabulary; several will also suggest that it requires specialized background knowledge. Those problems turn out to be only a small part of the difficulty. Here is the passage again, with the difficult words temporarily lifted: The smallest of the URF’s, and [A], has been identified as a [B] subunit 8 gene. The functional significance of the other URF’s has been, on the contrary, elusive. Recently, however, [C] experiments, as well as [D] studies, have indicated that six human URF’s [1-6] encode subunits of Complex I. This is a large complex that also contains many subunits synthesized in the cytoplasm. It may now be easier to survive the journey through the prose, but the passage is still difficult. Any number of questions present themselves: What has the first sentence of the passage to do with the last sentence? Does the third sentence contradict what we have been told in the second sentence? Is the functional significance of URF’s still "elusive"? Will this passage lead us to further discussion about