0948 02 1. Evidence is put forward that the bacterium Acinetobacter calcoaceticus, which use squinate as sole source of carbon and energy, degrades this compound via the β-ketoadipate pathway after transforming it into protocatechuate. 2. Extracts from cells grown on quinate can catalyse the oxidation of this hydroaromatic compound, and this activity can be measured by coupling it with the reduction of 2–6-dichlorophenolindophenol. The quinate dehydrogenase appears to be associated, at least to a significant extent, with particulated elements in the cell. 3. Cells grown on quinate can oxidize shikimate; furthermore, the optimum conditions under which crude extracts catalyse the oxidation of quinate and of shikimate are identical. In contrast to these observations the data obtained exclude the possibility that quinate is converted into protocatechuate by means of its previous transformation into shikimate.