Eighteen patients with advanced paranasal sinus carcinomas were treated by "two-route" intra-arterial chemotherapy using cis-diamminedichloroplatinum (CDDP) and sodium thiosulfate (STS) to preserve the hard palate and the eye. In these patients, 100 mg/m2 of CDDP was administered weekly through each feeding artery of the tumor superselectively at 5 mg/min. During infusion of CDDP, STS at a two-hundred fold dose of CDDP was injected through a catheter placed in the brachiocephic vein introduced via the subclavian vein. The complete and partial response rates were 14/18 (78%) and 4/18 (22%), respectively. None of the nine patients following operation showed residual tumors histologically. The peak of the mean total plasma platinum concentration was 5.5 micrograms/ml, and this concentration was rapidly reduced to 1.5 micrograms/ml in 5 hours. The peak of the plasma protein unbound platinum was 3.9 micrograms/ml. This concentration rapidly decreased to almost zero within 5 hours after IA infusion. The mean tumor platinum content achieved by superselective IA infusion was as high as 6.0 micrograms/g tumor, and this decreased rapidly to 2.4 micrograms/g tumor on the 5th day after the 1st intra-arterial infusion. All patients were free from chemotoxicity such as renal, hematological dysfunctions, or gastrointestinal symptoms. Each chemotherapy treatment could be done weekly on schedule. All but one patient was alive for 5-40 months. This new method of chemotherapy appears very effective for advanced paranasal sinus carcinomas.