The biotransformation of four alcohol substrates (butanol, 2-methylbutanol, 3-methylbutanol and 2-phenylethanol) into their acids was studied using a strain of Acetobacter aceti. Bioconversion yields depended on the molecular structure of the alcohol. Biotransformation of high concentrations of alcohols was possible until the precursor reached an inhibiting concentration (3.8 g dm(-3) for butanol and 3-methylbutanol, 4.2 g dm(-3) for 2-methylbutanol). In contrast, biotransformation of 2-phenylethanol decreased when alcohol concentration was higher than 0.3 g dm(-3). Dissolved oxygen concentrations and pH conditions of the medium were important factors in improving bioconversion. Transformation of 2-methylbutanol into the corresponding acid was increased when dissolved oxygen partial pressure increased from 60 to 80% and regulation at pH 6 allowed an increase in the production of butyric acid from butanol.