To study muscle necrosis due to prolonged limb compression, we measured intramuscular pressure by inserting wick catheters into 10 volar forearms and 10 anterior tibial compartments of adult volunteers. We then placed the subjects in positions in which victims of drug overdose are commonly found. Intramuscular pressures in the area of direct compression on hard surfaces ranged from 26 to 240 mm Hg, and averaged 101 mm Hg. Most remarkable was a mean pressure of 180 mm Hg on compression of the forearm by the rib cage. These pressures are sufficient to cause muscle and capillary ischemia and necrosis by local obstruction of the circulation. This local injury by limb compression may produce edema sufficient to start compartment tamponade and consequent muscle-compartment and crush syndromes.