Carbon sources utilized by virulent Treponema pallidum organisms extracted from infected rabbit tissue have been investigated. Utilization of 14C-labeled compounds by T. pallidum was monitored by degradation of these compounds to 14CO2. Experiments have consistently shown that of 22 carbon sources examined, [14C]glucose and [14C]pyruvate are selectively degraded to 14CO2 under the experimental conditions employed. When [1-14C]pyruvate, [2-14C]pyruvate, and [3-14C]pyruvate are tested, virulent T. pallidum preferentially degrade and release the carboxyl group as 14CO2. End product analyses indicate that CO2 and acetate are the major products of pyruvate degradation by T. pallidum.