Artificial swim bladder deflation was examined as a technique to increase postrelease survival of largemouth bassMicropterus salmoidescaught from deep water. Depressurization was simulated with a hyperbaric chamber. Largemouth bass showed clinical depressurization signs when depressurized from a simulated depth of 3.5 m and were unable to immediately submerge when depressurized from 8.4 m. When depressurized from a simulated depth of 10.5 m, largemouth bass experienced 0% mortality when subsequently held at 14°C but 78% mortality when held at 28°C. Survivors floated for more than 6 h, a response that could expose them to higher water temperatures in stratified lakes and to increased predation, illegal harvest, and injury. Depressurized largemouth bass that had their swim bladders deflated by being punctured with a hypodermic needle were able to submerge and experienced no mortality when transferred to 14°C or 28°C. The punctured swim bladders were functional immediately. Growth over 4 weeks did not differ significantly (P> 0.05) between largemouth bass with or without artificially deflated swim bladders, and no deaths occurred over this period. We recommend artificial swim bladder deflation for largemouth bass showing depressurization signs and caught from depths greater than 6 m.