The antimicrobial activity of a series of nitro-heterocyclic drugs was determined and correlated with a number of physicochemical properties. The best correlation is found with the polarographic half-wave potential, while the partition coefficient and LUMO-values contribute poorly to the relationship. The value of the dipole moments can be used to discriminate between active 2-nitro and 5-nitroimidazoles and inactive 4-nitroimidazoles. Free-Wilson analysis emphasizes the need of structural parameters like the presence of the nitro group in position 2 or 5 or a methyl substituent on the imidazole ring. The activity is enhanced by a vinyl group in position 2 and is decreased by the presence of a phenyl substituent.