Gulf toadfish (Opsanus beta) were continuously exposed as embryos, sac fry and juveniles to technical chlorpyrifos in two 49-day early life-stage toxicity tests. Survival was significantly (alpha = 0.05) reduced only in 150 micrograms/l). However, toadfish exposed to chlorpyrifos concentrations from 3.7 to 150 ug/l weighed significantly less than control fish: 9% lower in 3.7 ug/l to 62% lower in 150 ug/l. The 96-hour LC50 for juvenile fish was 520 ug/l. Concentrations of chlorpyrifos in toadfish and bioconcentration factors increased with increasing exposure concentration, a condition not generally observed with other marine fishes and other test chemicals. These results demonstrated the procedures for, and the practicality of, early life-stage tests with the marine species. The authors recommend the use of the gulf toadfish for comparative toxicity testing and for evaluating the toxicity of substances in conjunction with ontogenetical, physiological and histological investigations of the considerably studied genus. The authors do not recommend it for routine effects testing.