An experiment to gauge the effect of OK-432 on UFT activation under a combined administration of UFT and OK-432 at a therapeutic dose has been pursued clinically by determining the blood and intratumoral 5-FU concentrations after administration of UFT. UFT was administered orally to a group of AH-130-bearing rats at a dose of 12 mg/kg or 8 mg/kg. In another group that was given combined treatment with OK-432, the OK-432 was administered subcutaneously at a dose of 0.1 KE/kg together with UFT. The intratumoral 5-FU concentration at 4 hours after UFT 12 mg/kg administration showed higher values in th single UFT treated group than in the combined treated group, but at 8 hours no significant difference was found between these two groups as the concentrations were 0.133 +/- 0.027 microgram/g and 0.128 +/- 0.021 microgram/g, respectively. Further, no significant differences were noticed in the blood and intratumoral 5-FU concentrations between both groups after administration of UFT at a dose of 8 mg/kg. Clinically, the blood FT-207 and 5-FU concentrations after UFT administration showed no significant difference between the single UFT treated group and the combined OK-432 treated group, nor was there a significant difference in the intratumoral concentration. In summary, it is considered that OK-432 has little effect on UFT activation when UFT and OK-432 are administered in combination.