The carcinogenicity of N-(5-Nitro-2-furfurylidene)-1-aminohydan to in (nitrofurantoin, NF-153) was examined in (C57BL/6N×DBA/2N)F1 (BDF1) mice. Three hundred of mice were divided into three groups, each group consisting about 50 male and 50 female mice. Nitrofurantoin was given in powdered diet at dose levels of 0.3, 0.075, or 0 % to the respestive group of mice. The overall incidence of tumors in male and female mice was as follows: 0.3% NF group, 7.7 and 25.9%; 0.075% NF group, 1.9 and 16.7 %; in the control group, 22.6 and 29.6 %, respectively. In the male, the total incidence of tumors in two experimental groups and that of hepatic adenoma in 0.3% NF group was significantly decreased from that of control by p<0.05 and p<0.05, respectively. There was no significant difference in the female. The results in the present study conclude that nitrofurantoin is not carcinogenic in BDF1 mice.