Among a cohort of 454 consecutive patients who had undergone coronary revascularization with the internal mammary artery (from November 1984 to October 1987), postoperative angiography was performed in 86 (18.9%) (77 males and 9 females, aged 33-74 years; median age 56 years). The interval between operation and angiography ranged from one week to 26 months (median 47 weeks). The mean patency rate for the internal mammary artery grafts was 83.7% (72 of 86 grafts), the patency rate having increased from 71% in 1984/85 to 92% in 1987. In the same cohort the patency rate of venous grafts was 64.5% (78 of 121 aortocoronary venous grafts). Many asymptomatic patients refused follow-up angiography; the patency rate is therefore likely to have been higher for the entire cohort. The high patency rate and good long-term results for internal mammary artery grafts support the view that this type of graft is preferable to others for coronary revascularization.