The nutrient pathway to the flexor tendons within the digital flexor sheath of adult chickens was investigated using tritiated proline. There was no difference in the uptake of the radioactive tracer by free segment tendons (detached from blood vessels) and the intact tendon lying in synovium. The uptake of tracer by tendons isolated from the synovium (but with unaltered vascular attachments) was significantly less than by the intact tendons. Radioactive tracer not only diffused across the synovium into the tendon, but along the course of the tendon itself. There was no difference in the uptake of radioactive tracer by 2-week-old tendon grafts with and without adhesions.