The relationship between pyruvate utilization and acetoin production was elucidated by incubating Lactobacillus plantarum cells in buffered reaction mixtures which contained varying concentrations of pyruvate, glucose, and metabolic inhibitors.Pyruvate utilization was greatest at pH 4.5, was pseudo-first order with regard to pyruvate concentration, and was stimulated by glucose. Fructose, galactose, sucrose and lactose were also stimulatory, but maltose was not. The molar conversion efficiency for pyruvate to acetoin was 72-84% at pH 4.5, but only 37-45% at pH 5.5. Pyruvate utilization decreased when the metabolic inhibitors N,N' dicyclohexylcarbodiimide, carbonylcyanide m-chlorophenylhydrazone or 2,4 dinitrophenol were added to the buffers. These data suggests that energy, possibly in the form of proton motive force, is required for pyruvate utilization in L. plantarum.