To investigate the effects of carboxyethylgermanium sesquioxide (Ge-132) on the cyclophosphamide (CY)-induced immunotoxicity, hemagglutinin titer (HA-titer), splenic IgM plaque forming cells (PFC) and contact-delayed type hypersensitivity (CDTH) were assessed in mice. Ge-132 was orally administered alone (single dose of 300, 600, 900 mg/kg b.w.) or with CY (10 or 50 mg/kg, i.p.) to mice on the 2nd day before, simultaneously with, the 2nd day after immunization. Within Ge-132 alone-treated groups, HA-titer and PFC to SRBC were significantly and dose-dependently enhanced when compared with control group. HA-titer and PFC numbers suppressed by the treatment of CY alone were significantly restored by the concomitant treatment of CY and Ge-132. Also, Ge-132 significantly decreased DNFB-induced CDTH and inhibited the CY-enhanced CDTH. These results indicate that Ge-132 may be able to increase humoral immunity and inhibit the immunotoxicity by CY.