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 (α = 0.05) reduced only in 150 μg/liter. However, toadfish exposed to chlorpyrifos concentrations from 3.7 to 150 μg/liter weighed significantly less than control fish: 9% lower in 3.7 μg/liter to 62% lower in 150 μg/liter. The 96-hr LC50 for juvenile fish was 520 μg/liter. 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 this marine species. We 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 this considerably studied genus. We do not recommend it for routine effects testing.