The utilization of glucose, amino acids, fatty acids, bicarbonate, purines, and pyrimidines by the Reiter treponeme was studied by using carbon 14-labeled substrates. The distribution of carbon from the substrates into various cell components was determined. Radioactivity from labeled bicarbonate in the cellular protein was restricted to aspartic acid. The Reiter treponeme is capable of synthesizing glycine, serine, alanine, aspartic acid, glutamic acid, proline, and possibly ornithine. Phenylalanine, arginine, lysine, leucine, isoleucine, valine, threonine, and histidine do not appear to be synthesized by this treponeme. The Reiter treponeme cannot synthesize fatty acids, and thymine is not incorporated. Glucose is a major carbon and energy source. Arginine, histidine, serine, threonine, and glutamic acid are degraded by the Reiter treponeme and may serve as energy sources. It was calculated that exogenously supplied amino acids contribute 41 to 54% of the cellular material; fatty acids, 18%; and glucose, 28 to 43%.