Twelve healthy subjects were studied after single dose (200 mg p.o.) and 3 days (2 x 200 mg daily p.o.) indobufen treatment. Our findings indicated that in addition to well-known antiaggregant activity, indobufen significantly decreases thromboxane B2 and increases 6-keto-prostaglandin F1 after acute and short-term treatment. The activity of renin-angiotensin-aldosterone system and kallikrein-kinin system did not change significantly after both experimental periods. It seems also unlikely that atrial natriuretic peptide mediates the effects of the drug.