Data on physiological parameters such as hematocrit, hemoglobin, erythrocyte count and size, organ weights, body-water weight, plasma and blood volumes are given for hatchery-raised Salmo gairdnerii. Methods for obtaining the above data using fingerlings varying in weight from 9 to 29 g are discussed. Mean values reported are as follows: hematocrit 31.8; hemoglobin 6.51 g/100 ml blood; R.B.C. count 1.11 million/mm3; R.B.C. length 14.67 μ. Kidney, liver, and spleen weights as well as total body water, and plasma and blood volumes were found to be statistically valid factors of body weight. Straight-line regression equations are given for each. A comparison of these data with recent summaries of similar data is given and possible reasons for discrepancies are discussed.