Ticlopidine has been shown to markedly inhibit the platelet aggregability induced by ADP in control animals not receiving 3LL cells. Ticlopidine was administered orally at the selected dose (200 mg/kg/day), to the rodents using different dose schedules and the inhibitory effects on spontaneous lung metastases of the Lewis lung carcinoma were studied. Ticlopidine did not have any significant influence on the metastases formation and on the primary growth of 3LL, although it inhibited platelet aggregation in tumor-bearing mice. These data indicate that the antiaggregatory effects of ticlopidine are not related to an antimetastasic effect in our model.