A methodology for using the estuarine grass shrimp (Palaemonetes pugio) in life-cycle toxicity tests was successfully developed. Life-cycle exposures of juvenile shrimp (12 to 19 mm in rostrum-telson length) to the chlorinated hydrocarbon pesticide endrin were begun in November 1976 and completed in March 1977. After the juveniles matured and spawned, the effects on their progeny were determined. Tests were conducted in a flow-through seawater system, using a modified Mount and Brungs diluter. The average measured exposure concentrations were 0 (control), 0.03, 0.05, 0.11, 0.18, 0.38, and 0.79 micrograms endrin/litre seawater. The juveniles reached sexual maturity during the first two weeks of the exposure. Thereafter, a photoperiod regime was used to induce reproduction, and the effects of endrin on the survival, growth, and reproduction of the parent generation were determined. Larvae spawned by control and exposed parents were continuously exposed until the juvenile stage (7 to 20 m in rostrum-telson length). The effects on survival, length of larval development, and growth of the F1 generation were determined.