The cells of the purple nonsulfur bacterium Rhodopseudomonas palustris, Nakamura strain, are capable of oxidizing thiosulfate and sulfide both under the anaerobic conditions in the light and under the aerobic conditions in the dark. Regardless of the presence of thiosulfate in the medium, the cells contain thiosulfate reductase, rodanase, thiosulfate oxidase, and sulfite oxidase. However, the capability to oxidize thiosulfate and sulfide is induced in Rh. palustris after the cells have been incubated in the presence of thiosulfate for 2--4 hours. The process of induction is related to the synthesis of protein components. Decomposition of thiosulfate in Rh. palustris when its concentration in the medium is low (2--5 mM) is accompanied with the formation of an equimolar quantity of sulfate. When the concentration of thiosulfate is higher (10--20 mM), the products of its oxidation are tetrathionate and sulfate. Therefore, the metabolic pathway of thiosulfate in Rh. palustris depends on its concentration in the medium.