The efficacy of schizophyllan, a beta-1, 3-D-glucan with a beta-1, 6-linked D-glucose residue isolated from Schizophyllum commune Fries, in combination with local radiation therapy was investigated using C3H mouse squamous-cell carcinoma NR-S1. Male C3H/He mice were implanted with 10(5) cells of NR-S1 tumor on day 0. On day 9 after implantation, mice received electron irradiation with a dose of 5,500 rads. Intramuscular injection of SPG (1.0 mg/kg and 5.0 mg/kg) was then started from the day following irradiation and repeated 15 times at one-day intervals. The antitumor effect was measured by the tumor size and survival time. Significant tumor growth suppression and prolongation of life-span were observed in the group given radiation and SPG (5.0 mg/kg) in comparison with the group which received radiation alone. In histopathological examination of irradiated tumor sites, stromal reactions accompanied by a much greater degree of cellular infiltration consisting of mainly lymphocytes were observed in the group given combined radiation and SPG (5.0 mg/kg).