Exposing brook trout to various concentrations of chromium (Cr(VI)) for up to 22 months (including reproduction) significantly increased alevin mortality at 0.35 mg Cr/l and retarded growth of young brook trout at the lowest concentration tested (0.01 mg Cr/l). Eight month exposures of rainbow trout significantly increased alevin mortality at 0.34 mg Cr/l and also retarded growth at the lowest concentration tested (0.10 mg Cr/l). Exposures of brook trout lasting 22 months showed, however, that growth was only temporarily affected, and therefore, it was not used as an end point to measure the affects of chromium on either species. Reproduction, and embryo hatchability of brook trout were unaffected at Cr(VI) concentrations that affected survival of newly hatched alevins. The maximum acceptable toxicant concentration (MATC) for brook and rainbow trout exposed to Cr(VI) in water with a hardness of 45 mg/l (as CaCO3) and a pH range of 7-8 lies between 0.20 and 0.35 mg Cr/l. The 96-h LC50 for brook and rainbow trout was 59 and 69 mg Cr/l, respectively; therefore, the application factor (MATC/96-h LC50) for both species lies between 0.003 and 0.006.