Steroids incroporated into Oregon Moist Pellets were fed to steelhead trout ( Salmo gairdneri) to determine if growth could be enhanced. In 1976, steelhead trout were treated with 17 α-methyltestosterone, diethylstilbesterol, diethylstilbesterol plus clomiphene citrate, 17 α-methyltestosterone plus flutamide (4′-nitro-3′ trifluoromethyliosbutranilide), or flutamide from the onset of exogenous feeding. In 1977, steelhead trout were started on treated diets 1 month after the onset of exogenous feeding and received testosterone propionate, testolactone, methylandrostenolone, 17 α-methyltestosterone, flutamide, estradiol, or estradiol plus progesterone. Fish treated with flutamide (20 μg/g food) or diethylstilbesterol (5 μg/g) plus clomiphene citrate (15 μg/g) from the onset of exogenous feeding showed an increase in weight compared with controls. The androgens and other estrogens tested did not enhance the growth of steelhead trout. All compounds (except flutamide) fed to the fish from the onset of feeding caused abnormal sex ratios. Androgens induced more males while estrogens induced more females. 17 α-methyltestosterone (1, 5, 15, or 35 μg/g), 17 α-methyltestosterone (5 μg/g) plus flutamide (20 μg/g), testolactone (10 μg/g), and methylandrostenolone (10 μg/g) advanced spermatogenesis. 17 α-methyltestosterone (2 or 35 μg/g), testolactone (10 μg/g), methylandrostenolone (10 μg/g), or flutamide (20 μg/g) caused hypertrophied granulosa cells or atretic oocytes in some ovaries. Intersexes containing both testicular and ovarian tissue in the gonads were found in some fish treated with 17 α-methyltestosterone (5 μg/g), 17 α-methyltestosterone (5 μg/g) plus diethylstilbesterol (5 μg/g), 17 α-methyltestosterone (5 μg/g) plus flutamide (20 μg/g), or diethylstiblesterol (5 μg/g) plus clomiphene citrate (5 μg/g). 17 α-methyltestosterone at 1, 5, 15, or 35 μg/g caused significant linear dose-dependent increases in epidermal thickness. There were no differences in the RNA DNA ratio between treatments. We conclude from these studies that steelhead trout do not respond positively in terms of growth enhancement from steroid treatment as has been shown in other salmonids. However, the androgen antagonist, flutamide, may be a potential growth enhancer in steelhead trout and may also be used as an antiandrogenic compound when administered with an androgen.