This study examined the effects of temperature on the final stages of reproduction in rainbow trout, Oncorhynchus mykiss. Elevated water temperature (16\sp∘C) advanced ovulation and milt production. Holding fish at 16\sp∘C opposed to 10\sp∘C did not affect circulating levels of testosterone (T), estradiol (E\sb2), 17α,20β-dihydroxy-4-pregnen-3-one (17,20βP) or gonadotropin II (GtH II) in females, even though ovulation was advanced. Holding males at 10\sp∘C or 16\sp∘C also did not affect T, 11-ketotestosterone (11-KT), 17,20βP or GtH II levels. This suggests that temperature does not affect reproduction through simple endocrine changes. Elevated temperatures in early November advanced milt production, yet introduction to 16\sp∘C water in late November or early December had no effect, suggesting that temperature effects were time dependent. My studies suggest that deviations in water temperature may affect the final stages of gametogenesis in rainbow trout but have minor effects on reproductive hormone levels.