We investigated the toxicity of Kepone to, and uptake by embryo, fry, juvenile, and adult sheepshead minnows (Cyprinodon variegatus) using intermittent-flow toxicity tests. Concentration of Kepone and percentage of adult fish surviving in a 28-day exposure were: Control, 95%; 0.05 μg/liter, 95%; 0.16 μg/liter, 100%; 0.80 μ/liter, 78%; 1.9 μg/liter, 20%; and 7.8 μg/liter and 24 μg/liter, 0%. Concentration factors (concentrations in fish divided by concentrations measured in water) for adult fish averaged 5,200 (range 3,100 to 7,000). Symptoms of poisoning included scoliosis, darkening of the posterior one-third of the body, hemorrhaging near the brain and on the body, edema, fin-rot, uncoordinated swimming, and cessation of feeding. Adults surviving the first exposure were spawned, and the embryonic development, hatching, and survival and growth of fry and juveniles were monitored in a 36-day exposure to Kepone concentrations of 0.08, 0.18, 0.72, 2.0, 6.6, and 33 μg/liter. A significant number of embryos from adult fish exposed to 1.9 μg of Kepone/liter of water developed abnormally and died even when incubated in Kepone-free water. Kepone in water was not as lethal to progeny as to adults: 36-day LC50 for juveniles was 6.7μg/liter; 28-day LC50 for adults, 1.3 μg/liter. However, the average standard length of juvenile fish was significantly reduced by exposure to 0.08 μg of Kepone/liter of water; some fish developed scoliosis. Concentration factors in juvenile sheepshead minnows averaged 7,200 and increased from 3,600 to 20,000 as exposure concentrations decreased.