The bluegill, Lepomis macrochirus Rafinesque, was subjected to various concentrations of hydrogen cyanide to determine the effects on long-term survival, growth, egg production, and egg hatchability. Intermittent-flow experiments were conducted using adults, juveniles, and newly hatched eggs in separate tests. Egg production was most sensitive to hydrogen cyanide, and the highest concentration with no adverse effect was below 5.2 μg/liter HCN. Fry survival through the first 6 weeks followed in sensitivity with the no-adverse-effect level occurring between 15.6 and 19.4 μg/liter HCN.