A native membrane-bound form and a solubilized (purified) form of acetylcholinesterase were prepared from mouse brain, and the effects of nonionic surfactants on both solubilization of the bound enzyme and stabilization of the solubilized enzyme were investigated. For the solubilization of acetylcholinesternse from mouse brain membrane, treatment with surfactants was more effective than hydrolytic enzymes or a high ionic-strength treatment, and Triton X-100 was more efficient than an ionic surfactant. The Triton X-100-solubilized enzyme exhibited a lower K_m value (46.0 μM) than the membrane-bound enzyme (59.5 NM). This K_m value was not changed in the presence of Triton X-100. The Km value of membrane-bound enzyme decreased slightly (13%) to 51.8 μM in the presence of Triton X-100. The solubilized enzyme showed an increased (35%) V_(max) value after exposure to Triton X-100, while the V_(max) value of the membrane-bound enzyme was not significantly affected. Most of the nonionic surfactants tested effectively stabilized the solubilized enzyme. The stabilization effect of Triton X-100 increased in proportion to an increase in concentration of the surfactant, up to its critical micellar concentration. Nonionic surfactants having lower CMC values were generally more effective in the stabilization of the purified enzyme. This suggests that stabilization of solubilized acetylcholinesterase by nonionic surfactants is due to binding of the surfactants to the hydrophobic domain of the enzyme, thus keeping the enzyme in a micellar environment.