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Cyclochlorotine (CC) causes hepatic necrosis and has carcinogenic properties. The in vitro application of CC on myocytes induced disruption of myofibrils and large accumulations of actin, myosin, alpha-actinin, and vinculin at the cellular processes. This agent also induced the formation of islands of myosin and alpha-actinin aggregates. Actin filament bundles in fibroblasts were either unaffected or disrupted completely. CC damage was dose-dependently reversible. Acute administration of CC by intraperitoneal injection to rats caused degeneration and necrosis in hepatocytes revealing that the liver was a specific target. CC poisoning has shown to induce the formation of large accumulations of actin, myosin, _-actinin and vinculin at the cellular processes. It also induces the extensive formation of islands of myosin and _-actinin aggregates, scattered within the cytoplasm. The desmin distribution is changed from a loosely to a densely arranged filament network. Cytoplasmic microtubules remained normal and could not be distinguished from their usual pattern. Thus, the degree of CC influence on myofibrillar and cytoskeletal proteins seems to be in the order of actin, myosin/a-actinin/vinculin, desmin and tubulin. This order is proportional to the proximity of proteins to actomyosin of myofibrils. CC, in some as yet unknown manner, appeares to dismantle previously assembled myofibrils and to form aggregates of myofibrillar and cytoskeletal proteins. The accumulation of myoproteins, particularly actin, at the cellular peripheries was characteristic of CC treatment, but its mechanism remains to be clarified. Two different responses of fibroblasts were noted after CC treatment, i.e., actin filament bundles were either unaffected or were disrupted completely to result in the formation of actin islands. Also, cell damage caused by CC treatment is reversible. (A15416)