Athymic BALB/c nude mice, bearing a human melanoma LOX, were given the photosensitizing drug Photofrin II (10 mg/kg body wt.) intraperitoneally. The mice were also given one of the following chemicals intraperitoneally: glucose, galactose and glucose plus nordihydroguaiaretic acid (NDGA) which is an inhibitor of glycolysis. Multiple injections of glucose (3 g/kg body wt. given at -1, 0, +1 and +3 h relative to the injection of 10 mg/kg of Photofrin II at time 0) resulted in a significant increase in the uptake of Photofrin II in the tumor 4 h after a Photofrin II injection, while the uptake of Photofrin II in the other tissues remained unchanged. Administration of galactose had no significant effect on the uptake of Photofrin II in the tissues studied (tumor, muscle, skin and liver). NDGA seemed to abolish the effect of glucose injection.