Internal mammary artery (IMA) grafts have excellent long-term patency rate and result in improved late survival. Conventional use of IMA was only for selected cases. Elder or acute myocardial infarction case had been excluded from IMA use. During past 30 months we extended the indication of the IMA use for all the ACB case. The present study was undertaken to assess the possibility of routine use of the a IMA for aorto-coronary bypass (ACB). From Nov. 1987 through May 1990, we performed consecutive 110 ACB with the protocol "routine use of the IMA for all the ACB surgery". The 78 men and 32 women (29%) had a mean age of 64 years old (range 38 to 80 years old). Thirty-five patients (32%) were 70 years of age or older. Eighty-four patients had stable angina, nineteen patients had unstable angina, seven patients had acute myocardial infarction. IMA was used in 106 patients (96%). An average of 3.6 coronary arteries per patient were bypassed, and 1.6 distal anastomosis per patient were made with IMA. Combined cardiac surgery was performed in 8 cases (ventricular septal rupture repair: 2 cases, coronary endarterectomy: 4 cases, left ventricular aneurysm resection: 1 case, mitral commissurotomy: 1 case). Post operative complication due to IMA use were infrequent and operative mortality was 6.3%. In summary, routine use of the IMA for ACB surgery was possible method as if in high risked cases (elder or poor left ventricular function). We believe this method result in improved late result. We concluded routine use of the IMA for ACB was possible and usefull method.