Malignant pleural effusion is typical of complications in advanced lung cancer patients, most of whom complain of dyspnea. The standard treatment for symptomatic pleural effusion is intrapleural administration of a chemical agent. In Japan, OK-432, a streptococcal preparation, and cisplatin (CDDP) have been among the most frequently used chemical agents. There have been very few reports on the efficacy of chemical agents for malignant pleural effusion. We compared therapeutic efficacy and toxicity of intrapleural OK-432 with CDDP in a case-control study. The subjects consisted of 32 lung cancer patients with malignant pleural effusion who were admitted to our hospital between January 2000 and June 2004. The therapeutic efficacy was assessed from duration of chest drainage after intrapleural administration, response rate, time to progression of malignant pleural effusion, and survival time. No statistically significant difference was observed for therapeutic efficacy. Although the OK-432-treated group had only grade 1 fever, chest pain, nausea, the CDDP-treated group had a grade 2 increase in creatinine and grade 3 nausea. Intrapleural OK-432 seemed to be better tolerated in the treatment of malignant pleural effusion than intrapleural CDDP.