Reproduction of rainbow trout, Salmo gairdneri in acidic water was studied. Adults were exposed to waters of pH 4.5, 5.0, or 5.5 during the final 6 weeks of reproductive maturation; control acidities were pH 6.5-7.1. Progeny of acid-exposed females and control males had reduced survival through 7 d of development, hatching, and yolk-sac absorption, demonstrating that oogenesis is sensitive to acidic conditions. Similar reductions in the survival of the progeny of acid-exposed males and control females indicate the sensitivity of spermatogenesis to low ambient pH. Among the progeny of unexposed adults, survival through 7 d of development and hatching was lower during rearing at pH 4.5, 5.0, or 5.5 than at pH 6.5-7.1.