This study describes quantitatively the components of atherosclerotic plaques in native coronary arteries and in saphenous vein grafts used for aortocoronary bypass in women versus those in men. A total of 979 five-mm segments of native coronary arteries and 842 five-mm segments of saphenous veins was examined by computerized planimetric technique in 11 women and in 11 men, who were matched for survival time after the bypass operation and for age at death. Comparison of the mean percentages of the plaque components in the native coronary arteries and in saphenous vein grafts revealed that the atherosclerotic plaques in women contained significantly more cellular fibrous tissue compared to men, both in the native coronary arteries (38% vs 4%; p less than 0.001) and in the saphenous vein grafts 70% vs 36%; p less than 0.05). Dense fibrous tissue was significantly less in the plaques of the native coronary arteries in women compared to men (50% vs 85%; p less than 0.001) and in the plaques of the saphenous vein grafts (25% vs 57%; p less than 0.05). Cellular fibrous tissue is often found at an early stage of plaque development, whereas dense fibrous tissue is a major component in later stages. To elucidate possible reasons for the "younger" appearances of the plaques in the women compared to the men in both, native coronary arteries and saphenous venous conduits, further investigation is warranted.