Exposure of three generations of brook trout (Salvelinus fontinalis) to zinc concentrations ranging from 2.6 to 534 micrograms/liter produced no significant harmful effects. During a separate exposure of embryos and larvae, 1,368 micrograms Zn/liter significantly reduced (P = 0.05) both embryo and 12-week larval survival. An additional partial chronic exposure also resulted in significantly reduced (P = 0.05) egg chorion strength and embryo survival at 1,360 micrograms Zn/liter. The maximum acceptable toxicant concentration (MATC) for brook trout exposed to zinc in Lake Superior water (hardness = 45.4 mg/liter as CaCO3; pH = 7.0-7.7) lies between 534 and 1,360 micrograms Zn/liter. The 96-hour LC50 (median lethal) concentration for brook trout was 2,000 micrograms Zn/liter; thus the application factor (MATC/96-hour LC50) lies between 0.267 and 0.680. Brook trout gill, liver, kidney, and opercular bone tissues accumulated the greatest amounts of zinc. Edible muscle tissue did not accumulate zinc. Zinc loss from gill and liver from first-generation trout transferred to control water for 12 weeks was 55% and 59%, respectively, based on the total micrograms of zinc per whole tissue) zinc in kidney tissue (based on the total micrograms of zinc per whole tissue) increased 192%, however, during the 12 weeks in control water.