The method advanced for estimating prey-predator relations in reservoirs is based on fish standing crop data derived from samples collected in rotenone-treated coves in 23 reservoirs. The sampling, in August 1972 and 1973, was part of a cooperative study conducted under the auspices of the Reservoir Committee, Southern Division of the American Fisheries Society. Estimates were made of sizes ofprey species which predators with various mouth sizes could swallow; lengths ofall species ofpredators were then adjusted to equal the lengths of largemouth bass of equivalent predatory capability; and a computer program was develaped to calculate biomass of prey available to predators in length classes equivalent to 1-inch length classes of bass 1- to 28 inches long. Results indicated that 50% of the populations sampled were deficient in available prey. Stocking ofadditional predators in these instances would be deemed inadvisable.