Fifteen patients with clinical signs that could indicate a chronic compartment syndrome of the first dorsal interosseous muscle of the hand were investigated by pressure recording at rest and during exercise. Objective data, verifying such a syndrome, were found in four of the patients. Increased muscle relaxation pressure during exercise and intramuscular pressure at rest after exercise compared with normal pressure were well correlated to the development of the symptoms of chronic compartment syndrome. Fasciotomy of the first dorsal interosseous muscle relieved the symptoms and normalized the pressure.