Fingerling brook trout, Salvelinus fontinalis (Mitchill), were subjected to acute and chronic pH stress for maximum periods of 10 000 min in a series of dilutions of sulfuric acid or sodium hydroxide at 10 and 20C after acclimation at 15C and pH 6.8. Lethal limits of pH were estimated to be pH 3.5 and 9.8 at both temperatures. There were no observable differences in the resistance times at lethal pH stresses between test temperatures. The order of death was not significant in relation to length or weight of the fish.