19 patients were studied after operation for coarctation of the aorta. The average age at operation was 13.7 years. Crafoord's operation was performed in 16 cases and in the other three an aortic patch was necessary. The average post-operative period was 4.7 years. 14 cases were classified as good results: normal femoral pulses and arterial blood pressure. The other 5 cases were considered as unsatisfactory: 2 mediocre results with normal arterial blood pressure but diminished femoral pulses and oscillometric indices; 3 poor results with hypertension at rest. On exercise with bicycle ergometry the following results were obtained: the systolic blood pressure rose in a comparable manner to that observed in normotensive individuals of the same age on exercise except in 2 cases. These two patients had an aortic patch and one had a residual intraaortic pressure gradient. The pronostic significance of these findings is not known. However the use of an aortic patch is often associated with abnormal blood pressures at rest or on exercise. The fact that the majority of patients operated for coarctation of the aorta have normal blood pressure profiles on exercise should be emphasised.