Plasma cells obtained from the peripheral blood of a patient with multiple myeloma was incubated in serum and Krebs-Ringer bicarbonate buffer with 14C-labeled glucose, acetate, and propionate. Glucose utilization by these cells amounted to 0.5 μmole per hr per 108 cells and was mainly via the Embden-Meyerhof pathway, and only 6% or less traversed the hexose monophosphate shunt. The presence of Krebs cycle activity was demonstrated by direct isolation of several labeled intermediates after incubation with either 14C-acetate or 14C-propionate. The distribution of 14C in lactate, succinate, fumarate, malate, aspartate, and glutamate indicate a complete Krebs cycle. Acetate was metabolized via the Krebs cycle to the extent of 0.15 μmoles per hr per 108 cells, and the rate of propionate utilization was 0.17 μmoles per hr per 108 cells.