Thromboxane concentrations were investigated in the arterial plasma of 44 patients (25 smokers, 19 nonsmokers) with chronic obstructive arterial disease (COAD) of the lower extremities, documented by angiography. The thromboxane levels were measured by radioimmunoassay. The results indicate that smokers with COAD have significantly higher thromboxane levels than nonsmokers with COAD. The potential effect of nicotine on thromboxane is discussed.