Abstract The effects of 3 phenolics and of a homologous series of esters of para-hydroxybenzoic acid (the parabens) on Escherichia coli with known deletions in outer membrane lipopolysaccharide (LPS) are described. Of the phenolics, chlorocresol was the most active and phenol the least, with butyl p-hydroxybenzoate the most effective paraben. The most sensitive strain to the various inhibitors was usually a deep rough mutant (heptoseless LPS). Studies were also made with a chelating agent, ethylenediamine tetraacetate (EDTA) in combination with some parabens. EDTA potentiated, to some extent, the activity of the methyl and butyl esters, its activity depending upon the concentration at which it was employed.