Using information from published studies, the relative sensitivity of various freshwater fish to a range of chemicals was examined. Specifically, the objectives were to: (1) determine which species are used most often in toxicity tests, (2) assess the relative sensitivity of these species to various chemicals, and (3) determine whether the two most commonly tested species exhibit differences in their relative sensitivity to different classes of chemicals. Fathead minnows, rainbow trout and bluegill sunfish were the three most commonly used species in 96-h LC50 tests. Of the nine species examined, coho salmon and rainbow trout were the most sensitive species to 190 chemicals, while goldfish and carp were the least sensitive. Fathead minnows and rainbow trout were not equally sensitive to 13 different classes of chemicals; for example, while trout were significantly more sensitive to metals, fathead minnows were more sensitive to hydrocarbons. Such comparisons are expected to be useful for predicting the relative responses of different species to previously untested chemicals in such groups, and in gaining insight into physiological modes of action.