Annual reproductive cycles of largemouth bass (Micropterus salmoides) collected in the heated area of a 1120-hectare reservoir receiving thermal effluent were similar to cycles from bass collected in unheated waters during 1969 and 1970. Average maximum monthly temperatures at the heated area exceeded those in unheated waters by greater than 10 C for the 2 years. Few monthly differences in gonosomatic indices were found between heated and unheated areas. Earlier attainment of maximum gonadal size and the presence of significantly larger juvenile bass at the heated area suggested that reproduction might be accelerated by thermal discharge. However, gonadal condition indicated that the reproductive period started in March and continued through April in both areas. Reproduction may have been advanced in some heated-area bass, although this was not obvious from overall changes in the reproductive cycles of bass from unheated areas.