Techniques used to quantify circulating levels or stcroid hormones in teleostean fishes may help solve problems in fisheries research. Competitive protein binding assay used to determine levels of androgens. corticoids. and radioimmunoassay for estrogens allow analysis of relatively large numbers of samples within a short period of time. Results obtained by these methods indicate that rainbow trout (Salmo gairdlleri) have endocrine responses to various stressors. Repeated bleeding causes a marked lowering of plasma androgens in the male while cortlcoids arc increased in both sexes. Gonadectomy reduces androgens in the male more rapidly than in the female; estrogen levels are not appreciably altered. Carbon dioxide anesthesia greatly elevates plasma corticoids while tricaine methanesulfonate has no apparent effect on corticoids or androgens. Such information may be of use to researchers wishing to establish background levels of these hormones in extirpation experiments or in adminstration studies influencing the endocrine system. Steroid assays may also be of value in determining effects of sampling techniques or other experimental conditions.