Trimethyltin (TMT) chloride, administered to adult male Long-Evans hooded rats, produced a unique and distinctive behavioral syndrome consisting of spontaneous seizures, tail mutilation, vocalization and hyperreactivity. The LD50 for TMT was weight dependent; in large rats (e.g., 450 g), 7 mg/kg TMT produced significant weight loss and lethality, whereas in small rats (e.g., 250 g), 7 mg/kg produced neither weight loss nor lethality. TMT produced mild hypothermia and tremors. Results are discussed in comparison with kainic acid-induced morphological alterations and septal lesion-induced behavioral alterations. Histopathological evaluations of hippocampal tissue revealed cell loss that was largely confined to regio inferior pyramidal cells. TMT offers potential as a tool for investigations of limbic system structure and function.