Aqueous solubilities, octanol: water partition coefficients and Rm were determined for twelve glycolmonophenyl ether analogues. Their correlation with growth inhibitory activity towards eight bacterial, yeast and fungal species was assessed. Correlations were also sought between bactericidal activity and inhibition of respiration of E. coli suspensions with these physico-chemical properties. Variations in antimicrobial activity generally correlated well with aqueous solubility. Partition coefficients were found to correlate poorly with biological response with the exception of those correlations involving Gram-negative micro-organisms. Regression equations relating solubility to biological activity generally varied significantly between micro-organisms and for different biological responses with E. coli. This suggested the possibility of different problems of drug penetration in different microbial species and/or different sites of action for the various biological responses.