California grunion were continuously exposed as embryos and fry to technical chlorpyrifos in two toxicity tests conducted in the same exposure apparatus. The first test, a 35-day early life-stage (ELS) test, began with approximately 2.5-day-old embryos that were exposed in flow-through aquaria in darkness until hatching was stimulated on day 9 of exposure. The second toxicity test, a fry test, began with newly-hatched fry and lasted 26 days. Test water temperature ranged from 23 to 26C and salinity from 24.5 to 34 dissolved solids in sea water parts per thousand by weight. Results of the two tests were similar, indicating that exposure of embryos added little to the overall toxicity of chlorpyrifos to grunions. Percentage hatch of embryos was unaffected by the chlorpyrifos concentrations tested.