Radiofrequency hyperthermia (RFH) was applied to 21 adnexal cancer patients in combination with IP administration of CDDP (150 to 200 mg) 2 weeks or more after surgery. The instrument used, an OMR-ON HEH 500C, was shown by rectal temperature monitoring to produce sufficient intraperitoneal temperature elevation up to 40 degrees-41 degrees C. The serum level of filterable CDDP after IP infusion of CDDP (150 mg) followed by sodium thiosulfate rescue was basically the same irrespective of whether RFH was used. It reached a peak level of 2.06 +/- 0.48 micrograms/ml (n = 8) 1h after IP infusion, and gradually declined thereafter. No serious side effect except 3 cases of II- to III-degree burns was recognized. A slight increase in the incidence of prolonged vomiting and diarrhea was found with the RFH combination. This suggests an exacerbating effect of RFH on intestinal damage following CDDP infusion. As for any suppressive effect on reaccumulation of ascites, RFH might have a slight benefit in increasing the antitumor effect of CDDP in 90% of patients.