Salmonella typhimurium LT-2 can utilize propionate as its sole carbon source. Studies on growth, oxidation by resting cell suspensions and by permeabilized cells, suggest that the propionate is transported by the acetate system. This result was confirmed using labeled propionate and acetate. ATP-monocarboxylate phosphotransferase, acyl-CoA orthophosphate acyl-transferase, propionyl-CoA dehydrogenase, acrylyl-CoA hydratase, lactate dehydrogenase, phosphoenolpyruvate (PEP) synthase and PEP-carboxylase activities have been identified in extracts of cells grown on propionate. Mutants deficient in PEP-carboxylase and synthase are unable to utilize propionate. On the basis of results obtained, it seems that the propionate degradation pathway occurs via acrylate and that PEP-synthase and PEP-carboxylase are essential enzymes.