Several bioassay methods, responses, and end points were evaluated for use in determining the temperature requirements of northern pike embryos. Large differences in maximum embryo survival to hatch occurred among experiments that could not be attributed to effects of water temperature alone. Emphasis was placed on evaluating the relative effects of temperature on embryo survival by our correcting for differences in fertilization success among experiments. The most variable end point among experiments was the optimum temperature, while the most reproducible end point was the median tolerance limit (TL50). The lower and upper TL50s were 6.9 and 19.2 C for normal hatch and 6.3 and 19.9C for total hatch. The age of the embryo at the time of exposure had a great effect on these tolerance limits. Temperature shock, source of fish, and wet fertilization in hard and soft water had negligible effects on these tolerance limits. Recommendations were made for routine thermal bioassays for fish eggs.