Ten normal and twenty arteriosclerotic patients underwent two successive static continuous exercise tests: - 4 minutes holding of 30% maximum power - 1 minute holding of 60% maximum power. Simultaneous recordings were made of: - The Xenon 133 washout curve of the anterior tibial muscle, to assess the ischaemia induced by exercise and to measure the duration of the hyperaemic phase; - The continuous lactate level in the femoral vein, using an original electrode specific for these enzymes. The following parameters were retained; - Resting, peak and the surface of accumulation of lactate after exercise; - The appearance time and the duration of accumulation of lactate with respect to the length of the hyperaemic phase. The following conclusions are drawn: - The differences in the height of the peak of the serum lactate. The duration and the surface of accumulation of lactate were only significant in obviously arteriosclerotic patients in whom exercise had induced ischaemia. - From the dynamic point of view: the hyperaemic phase always preceded the phase of venous accumulation of lactate, in all groups, peak lactates levels always occured during the hyperaemic phase and the length of the accumulation phase was 2 to 3 times that of the hyperaemic phase; in this respect, there was a significant difference between obvious arteriosclerotic patients in whom exercise induced ischaemia, and a group of other arteriosclerotic and normal patients.