In a prospective study series of 167 patients with tube thoracostomy for spontaneous pneumothorax in 1993-1996, 32 patients (age range 16-79 years, mean age 45.5 years) were treated with autologous blood-patch pleurodesis for persistent air leak. In 27 (84%) of cases the air leak ceased within 72 h after the pleurodesis. The duration of air leak was significantly shorter (p < 0.01) than in simple drainage. Empyema developed in three cases, and two patients with failed pleurodesis required open thoracotomy. Minor complications, mainly fever and pleural effusion, occurred in nine patients. Neither analgesia nor sedation was required during or after pleurodesis. There was no recurrence of pneumothorax during 12-48 months of observation, whereas simple drainage was followed by recurrence in 22 patients. Blood-patch pleurodesis is a simple, effective and painless method in pneumothorax, but carries an increased risk of intrathoracic infection.