Nitrofurantoin,* N- (5-nitro-2-furfurylidene)-1-aminohydantoin, is one of a series of substituted furan derivatives having a nitro group at the 5- position in the furan ring and possessing antibacterial properties.† It is the first of this series of compounds to be used in human infections. After oral administration it appears in significant concentrations only in the urine ‡ its usefulness has, therefore, been limited to infections of the urinary tract, for which it has been used by a number of workers.§ Dodd and Stillman,17in 1944, showed that the addition of a nitro group in the 5- position to a large number of substituted furan derivatives markedly enhanced their antibacterial properties. Cramer and Dodd18extended these studies and showed that the action of compounds of this type is bacteriostatic but that under certain circumstances, or at higher concentrations, some of them may also be bactericidal. Enhancement of the antibacterial effect