To examine contribution of plasma fibrinogen concentrations to coronary atherosclerosis in Japanese, a cross-sectional study was conducted from 1991 to 1993 for 169 myocardial infarction cases and 1 : 1 matched references. All cases had one to three coronary vessels with 50 percent or more stenosis. References were chosen out of Osaka residents who had no cardiac event by matching sex and age ((+)-3 years) with cases. Mean (SD) values of plasma fibrinogen concentration were 322 (81) mg/dl in men and 377 (77) mg/dl in women for cases, and were 282 (56) mg/dl in men and 277 (48) mg/dl in women for references; mean plasma fibrinogen was significantly higher in cases than in references for both men and women. Furthermore, mean plasma fibrinogen was progressively higher as the number of stenotic vessels increased for men, and similar trend was seen for women. The case-reference difference remained significant even after adjusting smoking status, hypertension, serum total cholesterol, serum HDL cholesterol. Although plasma fibrinogen concentration was reported lower in Japanese than in American Caucasians, plasma fibrinogen is suggested to be a risk factor for myocardial infarction among Japanese as so among Caucasians.