The effectiveness of immunotherapy using a streptococcal preparation, OK-432, was evaluated for cervical cancer. The 382 eligible patients were stratified by presence/absence of surgical operation and clinical stage, and then, in each stratum, were randomly divided into two groups: an OK-432 treatment group and a control treatment group. The 3-year recurrence-free rates of 221 patients in the OK-432 group and 161 patients in the control group were 71.9% and 58.6%, respectively. The intergroup difference was statistically significant (P less than 0.05). Delayed skin reactions to phytohemagglutinin (PHA) and Su-polysaccharide extracted from Streptococcus pyogenes Su-strain (Su-PS) and peripheral lymphocyte counts were reduced within two months after the initiation of therapy in both groups. The observed immunological changes were apparently reversed by 3 months after the start of the therapy in the OK-432 group, but this took at least one year in the control group, with significant intergroup differences at 6 and 12 months of the therapy (P less than 0.01). These results indicate that OK-432 can be considered as one of the most effective and useful immunotherapeutic agents for cervical cancer.