Summary.A study of the range of organic compounds utilized as sole carbon source byAcinetobacter lwoffiiNCIB 10553 indicates that the organism isAcinetobacterA2 in the classification of Baumann, Doudoroff&Stanier (1968). NCIB 10553 resembles NCIB 8250 (‘Vibrio 01′, described by Fewson, 1967a,b). NCIB 10553 adapted to utilize acetylsalicylate does not grow with the lowern‐alkanes, whereas it does utilize some sugars, although after a lag, and grows readily on a number of aromatic and aliphatic carboxylic esters, including triglycerides, natural oils and fats and other compounds of pharmaceutical interest. Cell‐free extracts readily hydrolyse fatty acid esters of the mono‐ and dihydroxybenzoates and of catechol, quinol, phenol andp‐nitrophenol. They also simultaneously hydroxylate and decarboxylate salicylate, 2,3‐, 2,4‐, 2,5‐ and 2,6‐dihydroxybenzoate but only in the presence of NADH (or NADPH) and FAD. Some other aromatic acids are slowly oxidized und