Four antitumor nitrosourea derivatives under development in Japan are described. Among these, GANU and MCNU, having very similar structures to chlorozotocin, are water-soluble compounds, and CDL-7 and EBNU are rather insoluble in water. The latter two are before clinical trials, and like other nitrosourea derivatives, have a marked antitumor activity in mouse leukemia L1210. Though GANU and MCNU are in the stage of clinical studies, it seems premature to draw conclusions about them. Antitumor activity and pharmacologic studies on four nitrosourea compounds under development in Japan are reviewed. These compounds are: 1-(2-chloroethyl)-3-(beta-D-glucopyranosyl)-1-nitrosourea (GANU), 1-(2-chloroethyl)-3-(methyl-alpha-D-glucopyranos-6-yl)-1-nitrosourea (MCNU), DL-1(2-chloroethyl)-3-(hexahydro-2-oxo-azepin-3-yl)-1-nitrosourea (CDL-7), and 1,1'-ethylene-bis(1-nitrosourea) (EBNU).