We conducted a single-center, randomized, placebo-controlled trial to determine whether streptokinase instillations adjunctive to chest tube drainage reduce the need for surgery and improve outcome in patients with pleural empyema. Fifty-three patients (frank pus aspirated, 81%; microbiological agent cultured, 62%; mean effusion pH, 6.6 +/- 0.4) received antibiotic treatment, chest tube drainage, and once-daily pleural rinses with either normal saline or normal saline with streptokinase (250,000 IU). Nine patients were excluded for various reasons before pleural rinses were started. Streptokinase (n = 22) was instilled over 4.5 +/- 2 days and saline (n = 22) was instilled over 3 +/- 1.3 days. One patient in each group died during treatment. Clinical treatment success and need for referral to surgery were the main outcome measures. No difference was observed after 3 days. After 7 days, streptokinase-treated patients had a higher clinical success rate (82 vs. 48%, p = 0.01) and fewer referrals for surgery (45 vs. 9%, p = 0.02). No significant radiologic or functional differences were observed between groups during follow-up over 6 months. We conclude that intrapleural streptokinase adjunctive to chest tube drainage reduces the need for surgery and improves the clinical treatment success in patients with pleural empyema.