A study of the ecology of developing embryos of the Pacific surf smelt, Hypomesus pretiosus, was conducted. Embryos were maintained in the laboratory and the time to specific embryonic stages determined. There was no significant difference in survival between the groups (ANOVA, P = 0.53). Field observations indicated that embryos are spawned in patches in the upper intertidal zone near the time of high tide. They are attached to gravel substrates by the zona radiata membrane which ruptures and quickly turns inside out at the time embryos are fertilized. After several days of development embryos detach from the original spawning substrates and are washed seaward and down into the gravel substrate in the intertidal zone. However, there was no significant difference (ANOVA, P > or = 0.09) in the number of eggs found at each of 4 depth strata in the upper, middle and lower intertidal zones. (Copyright (c) 1988 by the University of Hawaii Press.)