Nitrofurans compounds and derivatives demonstrate antineoplastic activity in vitro as well as in vivo. Nitrofurantoin caused in vitro growth inhibition of a FANFT-induced murine bladder tumor (MBT2) and a human transitional cell carcinoma cell line (GIBB) in concentrations of 125 microM, 250 microM and 500 microM. The implantation and growth of MBT2 in the cauterized mouse bladder was inhibited by 250 microM nitrofurantoin. The bladder mucosa of two groups of C3Hf/HeHa female mice was electrically cauterized. In group I, 1 X 10(6) MBT2 cells were injected into the bladders of 42 mice, while in group II 1 X 10(6) MBT2 cells in 250 microM nitrofurantoin solution were injected into the bladders of 51 mice. Positive tumor implantation was seen in 25 bladders (59.5 per cent) of group I as compared to 15 bladders (29.5 per cent) of group II. All tumors in group I were large, occupying more than 50 per cent of bladder cross sectional area with 24 per cent showing extravesical extention. Sixty-six per cent of tumors in groups II were less than 25 per cent of bladder cross sectional area and 13.4 per cent had extravesical extention.