Silver nitrate pleurodesis as prevention against recurrence in primary spontaneous pneumothorax was started in our department on an empiric basis. In a controlled trial in 1981 the method was found to be as good as earlier stated, but the method has a high number of side effects and has never been widely accepted. In a prospective, controlled trial comparing silver nitrate pleurodesis with tetracycline pleurodesis, we found no differences in recurrence frequency, but the time of hospitalization was significantly longer in the silver nitrate group (p less than 0.05). Furthermore, we found a decrease of exudation and a decreased use of analgetics in the tetracycline group. As a consequence of the investigation, we have abandoned the silver nitrate method and now recommend tetracycline pleurodesis as the treatment of choice in primary spontaneous pneumothorax in patients with only tiny blebs on the surface of the lung.