The benefits of immunochemotherapy with a penicillin-treated, lyophilized preparation of Streptococcus pyogenes, OK-432 (Picibanil), were reassessed in patients with resected non-small-cell lung cancer through a meta-analysis based on data from 1,520 patients enrolled in 11 randomized clinical trials. All 11 trials were started before 1991, and the subjects had been followed up for at least 5 years after surgery and randomization. In these trials, standard chemotherapy was compared with the same therapy plus OK-432. The endpoint of interest was overall survival, and analysis was based on intent-to-treat population without patient exclusion. Data were analyzed using the Mantel-Haenszel method. The 5-year survival rate for all eligible patients in the 11 trials was 51.2% in the immunochemotherapy group versus 43.7% in the chemotherapy group. The odds ratio (OR) for overall survival was 0.70 (95% CI = 0.56-0.87, p = 0.0010). Analysis of four trials in which central randomization was performed also reconfirmed a significantly longer survival time for the immunochemotherapy group (OR = 0.66, 95% CI = 0.44-1.00, p = 0.049). Based on these results of meta-analysis, it is postulated that postoperative adjuvant immunochemotherapy using OK-432 might improve the survival of patients after resection of non-small-cell lung cancer.