We reviewed 395 patients with isolated hemo- or hemopneumothorax from penetrating injuries. All patients were treated with immediate insertion of a chest tube and drainage of various amounts of blood up to 1,500 ml. Forty-five patients (11 percent) were in hemorrhagic shock on admission to the hospital emergency room, and all were resuscitated with volume replacement. Twenty-one patients (5.3 percent) whose blood pressure decreased again were found on exploration to have lacerated internal mammary or intercostal arteries or major lung lacerations extending into the hilus. All other patients were treated aggressively with chest tubes, aspiration of residual blood and fibrinolytic enzymes until the lung was fully expanded. We conclude that the clinical course of patients with hemothorax after insertion of a chest tube should determine whether exploration is necessary or whether nonoperative treatment should continue.