Acetobacter aceti have been grown on ethanol under inhibitory conditions created by high concentrations of phenol. A defined medium with no vitamin or amino acid supplements has been used such that ethanol was the sole carbon substrate. The culture temperature was maintained at 30 degrees C while the pH was manually controlled to fall within the range 4.5-6.0 during ethanol consumption. Growth on ethanol at a few thousand milligrams per litre (below the known inhibitory level) resulted in a maximum specific growth rate of 0.16 h(-1) with a 95% yield of acetic acid, followed immediately by acetic acid consumption at a growth rate of 0.037 h(-1). Phenol was found to inhibit growth by decreasing both the specific growth rate and the biomass yield during ethanol consumption. On the other hand, the yield of acetic acid during ethanol consumption and the yield of biomass during acetic acid consumption remained constant, independent of phenol inhibition. A model is presented and is shown to represent the phenol-inhibited growth behaviour of A. aceti during both ethanol and acetic acid consumption.