Seventy-nine patients underwent repeat coronary angiographies five years after coronary bypass surgery. Ninety-eight of 122 inserted grafts (80%) were patent. Significant coronary obstruction (greater than 50% reduction of luminal diameter) developed in 43/79 patients (54%) and was associated with a longer duration of angina before surgery and a lower diastolic blood pressure at the five-year follow-up, but significantly related to such factors as age, sex, type of angina, previous myocardial infarction, hypertension, hyperlipaemia, diabetes or smoking. The total number of significant obstructions increased from 230 to 308 (34%). Progression of pre-existing changes to occlusion was common and the number of occlusions increased 95% in non-grafted arteries compared with 48% in grafted arteries until the five-year evaluation. Fifty-seven of 81 new significant obstructions (70%) were found in non-grafted coronary arteries. The proximal part of the right coronary artery was most commonly affected with 19/57 (33%) of these new obstructions. A significant stenosis regressed in three patients. At the five-year follow up, 74/79 patients (94%) had less symptoms than before operation and 27/79 patients (34%) were asymptomatic. Nine patients had no angina, despite non-bypassed significant obstructions. All grafts were patent in 25/27 asymptomatic patients (93%) and in 38/52 (73%) of those with angina. Two patients had no anginal symptoms, despite occluded grafts. One had sustained a myocardial infarction and the other had symptoms of left ventricular failure. Well-developed collateral vessels were observed in 15/27 asymptomatic patients (56%) and in 45/52 (87%) of those with angina. Recurrence of symptoms was related to progressive coronary disease, graft occlusions, obstruction of anastomoses, non-bypassed obstruction or combinations of these changes.