The paper deals with antiisomorphisms of endomorphism rings of modules close to free ones (those modules are strong generators, i.e., they contain free cyclic direct summands). A criterion for such antiisomorphisms to be induced by a Morita antiequivalence is obtained. Specifically, any antiisomorphism of endomorphism rings of progenerators (e.g., of matrix rings) is induced by a Morita antiequivalence. Bibliography: 9 titles. © 1997 Plenum Publishing Corporation.