Pirarubicin, a new antineoplastic antibiotic of anthracycline derivative, was injected into the pleural cavity in 15 patients with malignant pleural effusion. The dose of pirarubicin was 40 mg or 80 mg/body. All 15 patients were evaluable for both efficacy and toxicity. Since one evaluable patient received two courses of intrapleural administration of pirarubicin, we evaluated a total of 16 courses. Overall response rate was 81.3% with 7 CR cases, 6 PR cases and 3 NR cases. As toxicities, transient elevation of fever was observed in 81.3%, chest pain in 37.5%, appetite loss in 18.8%, nausea in 12.5% and bone marrow suppression in 6.3% of 16 courses, but no alopecia was observed. Between 40 mg group (n = 8) and 80 mg group (n = 8), no significant difference was observed in response rate, response duration, survival duration or toxicities except for fever. Fever over 38 degrees C was observed in all (100%) the 80 mg group, which was significantly higher than 50% in the 40 mg group. Response duration in cases with fever over 38 degrees C (n = 12) was significantly longer than in cases with maximum fever under 38 degrees C (n = 4). Intrapleural administration of pirarubicin was considered to be effective for the treatment of malignant pleural effusion without severe toxicities.