alpha-1-Antichymotrypsin (ACT) is a component of the amyloid deposits in Alzheimer's disease. To elucidate its biological activities in the central nervous system, dissociated cultures of rat cerebral neurons were grown in a serum-free medium containing ACT. The addition of ACT (0.1-1-mu-g/ml) enhanced survival of microtubule-associated protein 2-immunoreactive neurons under the culture conditions examined.