Twenty-two consecutive patients with malignant pleural effusions (MPE) were treated with intrapleural Corynebacterium parvum (CBP) associated with parenteral methylprednisolone (MP) to determine its effectiveness and the frequency and nature of adverse reactions. After thoracentesis, 7 mg of CBP (Coparvax Wellcome) in 20 ml of saline were injected into the pleural cavity. On the day of treatment, the patients were given 1 mg/kg i.m. of MP 30 min before thoracentesis. The effectiveness of pleurodesis was assessed as follows: (1) complete response (CR; total resolution of pleural effusion after 3 injections of CBP at the most); (2) partial response (PR; formation of asymptomatic loculated effusion). In 5 patients leukocytes, lymphocytes and monocytes were determined in pleural fluid (PF) and in blood (B) collected before and 7 days after CBP treatment. Two patients were unevaluable. Of 20 evaluable patients, 18 (90%) had a CR and 2 patients (10%) had a PR. Eleven of 22 patients (50%) had a fever. Three patients had prolonged and/or high fever. Seven of 22 patients (32%) had mild chest pain. None of the patients presented other side effects. Twelve of 21 patients (57.1%) had a PF pH > or = 7.30; 2 of these died a few days after the treatment, and 10 had favorable responses. The other 9 patients had a PF pH < 7.30: all had favorable responses. The leukocytes, the lymphocyte subsets, the monocytes, the NK lymphocytes, and their PF/B ratios did not differ significantly before and after CBP treatment. Our study confirms that intrapleural CBP is an effective and simple method to control MPE.(ABSTRACT TRUNCATED AT 250 WORDS)