The present study deals with the question whether an insufficient vascular supply of certain areas can be made responsible for ruptures in the biceps tendon. The macroscopic and microscopic examination shows that the blood supply of the tendon in the part most prone to ruptures that is in the bicipital groove is guaranteed even in older individuals. It is at least much better than in the intra-articular portion where ruptures are seldom observed. This means that mechanical components such as friction are dominant. The vascular factors seem to play a minor part.