The importance of hormone reservoirs in mature teleost eggs is unknown. To elucidate the effects of hormones on embryonic development, steelhead trout eggs, Oncorhynchus mykiss, were immersed in either cortisol, testosterone, or thyroxine at two different stages of development. Elevated concentrations of cortisol were detectable in the trout eggs or embryos after immersion. Eggs exposed to cortisol during water hardening hatched faster than eggs exposed at the eyed stage. Eggs that hatched faster had elevated cortisol and cortisol glucuronide concentrations at hatch compared to groups immersed at eyed or control groups. The dedine of these elevated concentrations of cortisol and cortisol glucuronide during embryonic development suggest conversion, clearance or both. Eggs exposed to cortisol at the earlier developmental stage did not appear to clear or convert cortisol as efficiently as those exposed at a later stage. Testosterone did not accelerate hatching in steelhead trout. Thyroxine accelerated hatching in eggs immersed at the eyed stages but had no effect when given at water hardening. These eggs that hatched faster were more synchronous in hatching time compared to other groups. Prior to exogenous feeding (50 days post fertilization, dpf), animals immersed in cortisol when eye pigments had higher mean condition factor (Kn) than other experimental or control groups, but this effect was gone by 83 dpf. However, at 130 dpf, cortisol groups that were immersed at the eyed stage were again heavier, longer, and more robust than other groups. At 50 dpf, animals immersed in thyroxine at water hardening were significantly longer and less robust (smaller condition factor, Kn). These effects disappeared by 83 dpf. / Graduation date: 1993