The solvent-tolerant bacterium Enterobacter sp. VKGH12 is able to grow in toxic concentrations of n-butanol up to 1.5 % (volume in volume) as the sole carbon and energy source. Morphology changes in the cells growing on increasing concentrations of n-butanol were observed. The size of the bacteria decreased with increasing concentrations of n-butanol, also leading to an enhanced ratio between the surface and volume of the cells. This is in complete contradiction to the reaction of glucose-grown cells to which n-butanol had been added as a toxin. Similar differences were found in typical adaptive responses to toxic organic compounds, namely changes in fatty acid composition of membrane lipids and the activity of catalase. In both cases, reactions depending on the n-butanol concentrations could be observed when the toxin was added to glucose-grown cells, whereas no reaction was observable when the cells were growing in n-butanol as the sole carbon and energy source. This is another proof for the observation that there are certain differences between the adaptive strategies of cells when adapting to high concentrations of a growth substrate and those when adapting to a toxin added to growing cells.