Pacific herring (Clupea pallasi) eggs were incubated in the laboratory at 13 different salinity–temperature combinations (ranges: 5–45‰ S, 4–14 C). Data were obtained on rate of development, larval length at hatching, percent total hatch, and percent viable hatch. Subsamples of larvae, held in their incubation media, provided data on posthatching survival and larval size at yolk sac absorption. Maximum percent viable hatch, larval size at hatching, and maximum survival to yolk sac absorption occurred in a trial at 16.41‰ S, 6.85 C. Optimum conditions were calculated by response surface analysis — maximum total hatch: 12.01‰ S, 6.46 C; maximum viable hatch: 16.98‰ S, 8.33 C; maximum length of newly hatched larvae: 20.00‰ S, 5.54 C. Maximum percent viable hatch of largest larvae in the shortest incubation period is estimated to occur at or near 16.98‰ S, 8.7 C. Abnormalities of the lower jaw were present in larvae from eggs incubated at temperatures of 4.0 and 4.71 C. Pacific herring eggs are considered euryhaline and stenothermal. A comparison of laboratory and field observations suggests that occurrence and abundance of herring is related to the availability and extent of spawning salinities between 8 and 28‰. Moreover, catch statistics suggest that population abundance in North American waters is associated with spawning temperatures of 5–9 C, abundance is limited by temperatures of 9–10 C, and the maximum temperature for spawning is about 10 C. From the current study, survival of viable larvae to yolk sac absorption would place the lower limit of thermal tolerance of Pacific herring eggs between 4 and 5 C.