The pathogenesis of skeletal muscle necrosis produced by Tityus Serrulatus venom was studied by means of light microscopy and electron microscopy. Wistar rats were inoculated subcutaneously, at some distance from the muscles under study, with a sublethal dose of scorpion venom. Samples were taken of the tibialis anterior muscles of both rear legs, 2, 7 and 24 hours postinoculation. Light microscopy analysis after 2 hours revealed certain changes identified as "delta lesions", and also the presence of hyperconcentrated muscle cells. Electron microscopy confirmed these lesions and also enabled us to identify a degree of discontinuity in the plasma membrane with a persistence of the basal membrane. Hyperconcentrated fibers could still be observed 7 hours postinoculation. Histochemical analysis revealed high levels of calcium within the fibers. 24 hours after inoculation with the venom, numerous phagocytic cells were found in the degenerated fibers. Muscle cells were also found to have undergone alterations indicative of an ischemic process. The most characteristic finding 7 days postinoculation was the appearance of regenerative fibers. After thirty days the muscles regained their normal appearance. It is suggested that Tityus Serrulatus venom induces myonecrosis by means of a twofold action: direct action, which gives rise in the first place to a rupture of the plasma membrane, permitting a massive entry of calcium this being a key factor in the process of cell lesion and an assumed indirect action due to ischemia.