The serum Lp(a) lipoprotein concentration in 103 healthy control subjects was determined by ELISA (TintElise Lp(a) kit, Biopool, Umea, Sweden). The distribution of Lp(a) in the controls was highly skewed (mean 132, S.D. 109, median 99 mg/liter), which is similar to the results previously reported. Serum Lp(a) level in 104 subjects who underwent coronary angiography was also measured. These subjects were divided into two groups: 59 cases of stenosis(-) and 45 of stenosis(+) groups. Lp(a) level of the stenosis(+) group (mean 235, S.D. 197, median 159 mg/liter) was significantly higher than that of the stenosis(-) group (mean 156, S.D. 133, median 123 mg/liter) and of the controls (Wilcoxon test, p less than 0.05 and p less than 0.01, respectively). Further, stenosis(+) group was divided into three subgroups: 20 with single vessel disease, 13 with double vessel disease and 12 with triple vessel disease subgroups. Lp(a) level was correlated with the number of stenotic coronary vessels (Spearman's rank correlation coefficient, p less than 0.05). These results suggest that Lp(a) may play an important part as a risk factor for coronary heart disease.