The growth of Acinetobacter calcoaceticus 69-V on the alcohols ethanol, n-propanol, n-pentanol, n-hexanol and on phenol caused an alteration in its fatty acid composition leading to a gradual increase in the degree of saturation of the C16 acids from 55.4% to 83.5%, which (apart from phenol-grown cells) correlated to an increase in the resistance of the electron-transport phosphorylation against the effect of 2,4-dinitrophenol. These changes are in principle paralleled by changes observed when the growth temperature was increased in the sequence 20, 30 and 40 degrees C with acetate as the carbon and energy source. However, in cells grown at 40 degrees C, as in the case of phenol-grown cells, resistance decreased. This effect could be caused by an increase in the fluidity of the target membrane since, by contrast, the increase in sensitivity induced by growth at 40 degrees C can be partially annulled by provoking a decrease in fluidity by performing the inhibition measurements at a lower temperature (20 degrees C). Both the degree of saturation of the fatty acids and the fluidity of the cytoplasmic membrane are features that should enable the resistance of Acinetobacter calcoaceticus 69-V to xenobiotics to be predicted.