AbstractDetailed growth curves based on progressive turbidity readings have been used to study the inhibition of Aerobacter aerogenes Type I, by a series of alkyl 4‐hydroxybentoates. Results in the lag phase are irregular, but it is apparent that the elongation of this phase becomes very marked at the higher concentrations of the inhibitor and that complete inhibition of growth occurs at a concentration that extends lag indefinitely rather than at one which reduces the growth rate to zero. Inhibition in the logarithmic phase, plotted as a function of inhibitor concentration, gives curves convex to the abscissa that contrast with experience of fungi, where characteristic concave adsorption forms have been obtained. However, the convexity of the present series of curves is likely to be a reflection of secondary effects associated with this method of determining bacterial inhibition, particularly in that there is a loss of viability in cells exposed to the higher concentrations. Determinations based on stationary populations arc convenient and give good agreement between experiments, but are not necessarily related in any simple fashion to growth rate inhibition.Although the order of increasing activity with increasing chain length of the esters is similar that found for fungi the activity of the methyl ester is less against Aerobacter aerogenes so that solubility difficulties soon prevent the attainment of a reasonable level of inhibition.Growth curve methods that use a relatively small inoculum with consequent lag phase of variable length do not appear well suited for a direct study of growth rate inhibition.Growth curve method that use a relatively small inoculum with consequent lag phase of variable length do not appear well suited for a direct study of growth rate inhibition. A simple method better suited to this purpose is being developed.