The sheepshead minnow (Cyprinodon variegatus) was continuously exposed for 23 wk to the organochlorine insecticide endrin, from the embryonic stage through hatching until adulthood and spawning. The resultant progeny were monitored to determine the effects of the toxicant on their survival, growth, and reproduction. Average measured exposure concentrations were O (control), 0.027, 0.077, 0.12, 0.31, and 0.72 micrograms/liter. Embryos exposed to 0.31 and 0.72 micrograms/liter hatched early; all fry exposed to 0.72 micrograms/liter died by day 9 of exposure. At 0.31 micrograms/liter, fry were initially stunted and some died. Survivors seemed unaffected until maturity, when some females died during spawning; fewer eggs were fertile and survival of exposed progeny decreased. No significant effects were observed throughout this fish's life cycle at an exposure concentration of 0.12 micrograms/liter. Four-week-old juvenile fish accumulated 2,500 times the concentration of endrin in the exposure water; adults, 6,400 times; and their eggs, 5,700 times. The specific application factor (calculated by dividing the limits on the maximum acceptable toxicant concentration, >0.12 and <0.31 micrograms/liter, by the concentration lethal to 50% of the juvenile fish in 96 hr, 0.34 micrograms/liter) ranged from 0.35 to 0.91.