Intrapleural instillation of tetracycline as a preventive measure against recurrence in spontaneous pneumothorax was performed at the Department of Thoracic and Cardiovascular Surgery, Kyungpook National University Hospital for 3 years from Jul. 1984 to Aug. 1987. In this period, 124[70.0%] out of 177 patients of spontaneous pneumothorax who received closed thoracostomy were followed up. Tetracycline pleurodesis was applied to 32 cases. The recurrence rate of the tetracycline instillation group was lower than that of noninstillation group. In patients with first attack, the recurrence rate was 12.5% in the instillation group and 35.3% in the noninstillation group. In the second episodes, 25.6% and 83.3%[p< 0.01], in the third episodes 25.0%, 100.0%[p< 0.05]. In total cases, 18.8% and 39.8%[p< 0.05] of recurrence rates were observed. Systemic or local reactions such as fever, chest pain, and pleural effusion were observed in 23 patients[71.9%] after instillation, but all were transient and benign without sequelae. In cases of systemic or local reactions the recurrence rate was lower than that with no reactions but with no statistical significance. In the four patients primarily treated with tetracycline pleurodesis who then underwent thoracotomy, mild alterations were shown in the pleurae except dense adhesions at the previous thoracotomy sites. There was no significant difference between the two groups in terms of durations of hospitalization and post-treatment recurrences.