Fathead minnow larvae (Pimephales promelas) were exposed to triphenyltin hydroxide (TPTH) during brief (single pulse) or continuous exposure in 96-h and 30-day toxicity tests. The continuous exposure 96-h LC50 value was 7.1 microg/liter. Brief exposures for 12 to 72-h gave 96-h LC50 values that ranged from 61.8 to 6.0 microg/liter, respectively. The continuous exposure 30-day chronic effect concentration, based upon reduced growth, was 0.23 microg/liter. Survival was significantly reduced at 2.0 microg/liter. Brief exposures for 24, 48, and 72-h in 30-day tests significantly reduced survival and growth at 13.0, 13.0, and 60.0 microg/liter, respectively. It is suggested that both toxicant concentration and exposure duration are important factors to consider in the risk assessment of potential pesticide hazards in the environment. (Copyright (c) 1988 Elsevier Applied Science Publishers, Ltd.)