Some lakes with an historical record of fish populations have undergone acidification and fish no longer exist in these systems. Toxicity data suggest that the inability of fish to survive in these acidic environments is due to increased concentrations of hydrogen ion (H+) and aluminum (Al+++) in the water column. To reestablish fish populations in lakes of this kind it is necessary to (1) determine that fish are no longer present, (2) demonstrate that fish either cannot or have limited potential to survive in the systems, and (3) change the water quality, and demonstrate increased survival of fish under differing chemical conditions. We examined two acidic lakes (Woods Lake, pH ~5.0 and Cranberry Pond, pH ~4.8) for the first two conditions by conducting fisheries surveys and in situ bioassays using fingerling (age 0) brook trout (Salvelinus fontinalis). Woods Lake was also stocked with brook trout in the fall of 1984 and overwinter survival of two age classes determined. Emigration from the lake accounted for a relatively small percentage of the approximately 90 percent mortality in these stocked fish over winter. Neither acclimation procedures or experimental selection of brook trout for acid tolerance improved survival. Prior to, during, and after calcium carbonate addition to the lakes in the early summer of 1985 an extensive series of in situ bioassays was conducted that showed significantly improved survival of both age 0 and 1 brook trout after liming. Interactive effects of temperature, pH, and aluminum levels were evident during these experiments. No detrimental effects of liming on fish survival were observed.