The stability of plasmids in Lactobacillus plantarum was investigated by extended incubation of bacterial cells in the presence of different carbohydrates. Strain caTC2, carrying a plasmid-encoded chloramphenicol-resistant (CM(r)) phenotype, was grown overnight (16-18 h) in MRS, MRS-L, and MRS-M broths containing 2% glucose, lactose, and maltose respectively at 30-degrees-C. The cultures were subsequently held at 30-degrees-C and room temperature (21 +/- 1-degrees-C) for an extended period (7 days). The total viable cell counts were assayed on MRS agar plates and tested for sensitivity to 30-mu-g chloramphenicol/ml by replica plating. The plasmid profiles of the chloramphenicol-sensitive strains showed that there was a loss of the 8.5-kb plasmid,but not the 10.6 or 6.5 kb plasmids. Concomitant loss of the chloramphenicol resistance phenotype and plasmid at high frequency, particularly by using MRS-L at 21-degrees-C method, suggests that this would be a simple and efficient method for curing selected plasmids in lactobacilli.