Coho salmon (Oncorhynchus kisutch), alewife (Alosa pseudoharengus), spottail shiner (Notropis hudsonius), and rainbow smelt (Osmerus mordax) were exposed for 30 min to residual chlorine. The alewives were tested at 10, 15, 20, 25, and 30 C, the salmon and shiners at 10, 15, and 20 C and the smelt at 10 C. Thirty-minute LC50 values were both species- and temperature-dependent. All species showed an inverse relationship between test temperatures and LC50 values. The range of LC50 values observed, with the test temperatures in parentheses, were coho salmon, 0.29 (20 C)-0.56 mg/liter (10 C); alewife, 0.30 (30 C)-2.27 mg/liter (15 C); spottail shiner, 0.53 (20 C)-2.41 mg/liter (10 C); and smelt, 1.27 mg/liter (10 C).