1-(2-Chloroethyl)-3-isobutyl-3-(beta-maltosyl)-1-nitrosourea (TA-077) was hydrolyzed to its glucosyl metabolite TA-G by homogenates of guinea pig organs, rabbit VX-2 carcinoma and rat Yoshida sarcoma. The rate of TA-G formation by the kidney was the highest among the tissues examined and that by the diluted blood was undetectably low, reflecting their maltase activities. TA-077 was also hydrolyzed by suspensions of Yoshida sarcoma, AH130 hepatoma, L1210 leukemia, P388 leukemia and DBLA-10/C leukemia cells. The rate of TA-G formation was increased 10 fold by homogenizing the tumor cells. TA-G was taken up by the tumor cells much more efficiently than TA-077, explaining the higher sensitivities of the cultured tumor cells to TA-G than to TA-077. However, neither the maltase activity nor the membrane permeability to the drugs was a factor influential enough to explain the differences in drug sensitivity among the tumor cell lines.