(Newcomb 1978).Newcomb's data are extensive,represent reasonably large sample sizes (15 to 25),and are probably good approximations of Columbia River steelhead. The mean plasma Na+and K+values of the chelan Hatchery steelhead were within normal limits (Table 3,Figure 2)at the time of release.The Na+levels increased in seawater,but returned to normal (in the survivors)after 1 week. Hematology There is considerable hematological data in the literature for rainbow trout,less for steelhead trout.From the data summarized in Table 5,it may be possible to estimate the range of hematocrit and hemoglobin values for healthy steelhead.The lower limit of mean hematocrit should not fall below 30X,and mean hemoglobin values below 6 would certainly be suspect. Upper levels are more difficult to define.Snieszko (1960)reports mean hematocrits of 538 and mean hemoglobin levels of 8.7 g/100 ml of blood in rainbow trout of a size comparable to large steelhead smolts.Although our values on steelhead trout (Table 3)were much closer to Snieszko's,Newcomb (1978)reported mean hematocrit levels in steelhead similar to that found by other researchers working on rainbow trout (Table 5).A number of authors (McCarthy et al.1973;Wedemeyer and Nelson 1975;Wedemeyer and Yasutake 1977)repeatedly suggest that the hematocrit levels of clinically healthy rainbow trout should be between 24 and 438,with hemoglobins ranging from 5.4 to 9.3 g/100 ml blood,and these values will be used as the expected range for individual fish for the purposes of this report. The summarized data of the hematocrit and hemoglobin values for the Chelan Hatchery steelhead are presented in Figure 3.There was no difference in mean hemoglobin between 1978 and 1979 (8.9 g/100 ml)nor in 13 (Newcomb 1978). Newcomb's data are extensive, represent reasonably large sample sizes (15 to 25), and are probably good approximations of Columbia River steelhead. The mean plasma Na+ and K+ values of the Chelan Hatchery steelhead were within normal limits (Table 3, Figure 2) at the time of release. The Na+ levels increased in seawater, but returned to normal (in the survivors) after 1 week. Hematology There is considerable hematological data in the literature for rainbow trout, less for steelhead trout. From the data summarized in Table 5, it may be possible to estimate the range of hematocrit and hemoglobin values for healthy steelhead. The lower limit of mean hematocrit should not fall below 30X, and mean hemoglobin values below 6 would certainly be suspect. Upper levels are more difficult to define. Snieszko (1960) reports mean hematocrits of 53% and mean hemoglobin levels of 8.7 g/100 ml of blood in rainbow trout of a size comparable to large steelhead smolts. Although our values on steelhead trout (Table 3) were much closer to Snieszko's, Newcomb (1978) reported mean hematocrit levels in steelhead similar to that found by other researchers working on rainbow trout (Table 5). A number of authors (McCarthy et al. 1973; Wedemeyer and Nelson 1975; Wedemeyer and Yasutake 1977) repeatedly suggest that the hematocrit levels of clinically healthy rainbow trout should be between 24 and 43%, with hemoglobins ranging from 5.4 to 9.3 g/100 ml blood, and these values will be used as the expected range for individual fish for the purposes of this report. The summarized data of the hematocrit and hemoglobin values for the Chelan Hatchery steelhead are presented in Figure 3. There was no difference in mean hemoglobin between 1978 and 1979 (8.9 g/100 ml) nor in 13