The aim of this study was to unravel the identity of compatible solutes accumulated by Lactobacillus plantarum subjected to osmotic stress. Betaine was accumulated simulataneously with a novel compatible solute identified as carnitine, both present in the complex medium applied in this study. Beef extract provided the main source of carnitine in the medium. Both carnitine and betaine were accumulated to maximum concentrations of 248 and 231 μmol.g dry weight-1, respectively. A defined medium was devised devoid of carnitine. Addition of 0.5 mM carnitine to this medium increased the growth rate from 0.1 h-1 to 0.2 h-1 in media with 0.4 M sodium chloride. Also, carnitine made the organism more tolerant to sodium chloride. Growth occurred even when the sodium chloride concentration was raised from 0.5 M to 1.0 M. Quaternary compounds resembling the structure of carnitine and betaine enhanced the growth yield as well. γ-Butyrobetaine and succinylcholine restored the growth yield up to respectively 91 and 96% compared to non-stressed cells.