The aliphatic organo-metal derivative, trimethyltin, causes marked morphological damage to the CNS when administered by the intragastric route. Behavioral consequences of [CH3]3Sn treatment were described. Saline (0.9%) or 7.0 mg/kg [CH3]3SnCl was injected intragastrically in male Long-Evans rats divided into 2 groups of 9 each. Open-field activity during a 2 min interval was measured for each rat 40 days later. Following activity testing, the animals were trained to press a lever for food reinforcement on an ascending fixed-ratio [FR] series ranging from 2-99. Rats treated with [CH3]3SnCl were 3 times as active as controls in the open field and emitted lever responses at a significantly higher rate than controls throughout the FR series regardless of the reinforcement schedule. The possible neuropathological consequences and the relative permanence of the neurobehavioral changes following Sn treatment were discussed.