The catabolism of several amino acids has been studied with resting cells of various strains of acetic acid bacteria. In strong contrast to their pronounced carbohydrate oxidizing capacities, these bacteria possess only limited abilities to catabolize amino acids. All strains from the biotypeAcetobacter aceti and the acetate-oxidizing strains of the biotypeGluconobacter oxydans oxidize L-alanine often to near-completion. Most of them oxidize L-glutamic and L-aspartic acids, but on the whole much more slowly. Some strains also oxidize serine, threonine and proline weakly. All other amino acids investigated are not attacked. With several strains the deamination was investigated. Only those amino acids are deaminated, which can be oxidized. Resting cells of the biotypeGluconobacter oxydans which are unable to oxidize acetate (the suboxydans group according toFrateur) are likewise unable to oxidize, to deaminate and to assimilate any amino acid supplied. A simple procedure to determine quickly whether a strain belongs in the latter group, consists in following the uptake of O2 in the Warburg respirometer with L-alanine and acetate (no oxidation) and with ethanol (oxidation to acetic acid).