Air leakage persisted from the lung in three cases of spontaneous pneumothorax. Pleurodesis with autologous blood ended in failure. Autologous blood plus OK-432 was instilled into the thoracic cavity from the chest drainage tube. Air leakage was stopped without serious side effects and the chest tube was removed uneventfully. Although the long-term outcome of this treatment is not known, pleurodesis using autologous blood plus OK-432 may be an effective way of treatment for spontaneous pneumothorax in cases with high surgical risk.