Intramuscular pressures were measured in 12 patients with symptoms of medial tibial syndrome and in 12 patients with chronic anterior compartment syndrome. Measurements were performed with the wick catheter technique simultaneously in the deep posterior and the anterior tibial muscle compartments before, during, and after exercise. In the deep posterior compartment there was no pressure increase during or after exercise as compared to controls in either patient group. However, a significant pressure increase was present in the anterior tibial compartment during and after exercise in the patients with chronic anterior compartment syndrome as compared to normal resting values. The medial tibial syndrome patients demonstrated in the anterior tibial muscle compartment, exercise and post-exercise pressures, which were between those of the healthy controls and the chronic anterior compartment syndrome patients. The so-caLled medial tibial syndrome is probably not a compartment syndrome in the deep posterior muscle compartment. Intramuscular pressure measurement is a valuable tool in diagnosing a chronic compartment syndrome and in selecting patients in whom fasciotomy of the affected compartment is indicated.