The antitumor activity of 1-(2-chloroethyl)-3-isobutyl-3-(beta-maltosyl)-1-nitrosourea (TA-077), a novel water-soluble nitrosourea derivative, against leukemia L1210, Ehrlich carcinoma, sarcoma 180, Lewis lung carcinoma, Yoshida sarcoma, rat ascites hepatomas and Walker 256 carcinosarcoma was examined and compared with those of 3 reference nitrosourea antitumor agents, 1-(2-chloroethyl)-3-(beta-D-glucopyranosyl)-1-nitrosourea, 3-[(4-amino-2-methyl-5-pyrimidinyl)methyl]-1-(2-chloroethyl)-1-nitrosourea hydrochloride and 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea. TA-077 exhibited a broad antitumor spectrum against the above tumors. Among these 4 nitrosoureas, TA-077 produced the best therapeutic ratios (OD/ILS30) against leukemia L1210, irrespective of the administration route and schedule employed. The ratio obtained by consecutive treatment (ip) was superior to that by single administration, a unique characteristic of this novel nitrosourea agent. The inhibitory effect of TA-077 on the growth of non-syngenic tumors (solid form) was also significant in all administration routes employed (ip, iv and po). Furthermore, TA-077 showed a marked life-prolonging effect on both early and advanced forms of Lewis lung carcinoma.