The working status of 1165 patients aged 59 years or less (mean 49.8 years) was evaluated 7 to 77 months (mean 36 months) after aortocoronary bypass surgery. Although 76% of the patients eventually returned to work, only 56% were working 6 months after their operation. The proportion of patients working peaked at 2 years after the operation (at 66%) and decreased progressively to 56% at 4 years and 53% at 5 years without ever reaching the proportions that applied 12 and 6 months before the operation (84% and 69% respectively). Multivariate analysis identified three socioeconomic and three clinical variables as predicting the working status at 6 months and at yearly points during the first 4 years after the operation. Of the socioeconomic variables analysed, preoperative unemployment of long duration, a preoperative occupation that required strenuous physical effort and a low level of education were, in that order, the strongest predictors of postoperative unemployment. Among the clinical variables, associated noncardiovascular illness and the severity and duration of angina pectoris independently influenced the patients' post-operative working status. The authors conclude that modification of some of these variables should by attempted both before and after aortocoronary bypass surgery to see whether the rate of return to employment after the operation can be improved in selected patients.