Embryos of the inland silverside, Menidia beryllina, were exposed to the organophosphorus pesticide terbufos at nine combinations of temperature (20, 25 and 30 C) and salinity (5, 12.5 and 20 levels of salinity). Nominal exposure concentrations were 12.5, 25, 50 and 100 microgram terbufos/1 with an acetone and seawater control for each temperature/salinity combination. Test durations were temperature dependent and ranged from 5 to 14 days. Endpoints were embryo survival, hatching and percentage of larvae with normal vertebrae. Survival was significantly (alpha = 0.05) lower in tests conducted at 20 C for all salinities. Salinity affected survival only at combinations of 20 levels of salinity and 100 microgram terbufos/1. Both temperature and salinity affected the percentage hatch, with the lowest hatching occuring in 20 C tests, and in tests conducted at 20 levels of salinity. Anomalies in the development of vertebrae occurred across all temperature/salinity combinations.