The ex vivo effect of oral administration of ticlopidine on rat neutrophil chemotaxis was evaluated. Rats received either 3 oral doses (100 mg/kg body weight) of the drug, within a period of 48 h, via a gastric tube, or the drug was administered in drinking water for 14 days at a dosage of 75 mg/kg/day. Absorption of the drug was manifested by significant inhibition of adenosine diphosphate- (ADP-)induced platelet aggregation. No impairment of neutrophil chemotaxis toward zymosan-activated serum was observed in the ticlopidine-treated animals. These results indicate that concentrations of ticlopidine that significantly inhibit platelet function in rats are without effect on neutrophil chemotaxis toward zymosan-activated serum.