Poly-beta-hydroxybutyrate was determined in lactic acid bacteria belonging to the genera Lactobacillus, Lactococcus, Pediococcus and Streptococcus. Lactobacilli were grown in MRS broth, the others were grown in Elliker broth medium. Cell biomass was obtained by centrifugation. The cell walls were lysed with sodium hypochlorite. Poly-beta-hydroxybutyrate was extracted using chloroform in a Soxhlet system. Then it was converted to crotonic acid using sulfuric acid and the amount of crotonic acid was measured spectrophotometrically. The yield of poly-beta-hydroxybutyrate (% of cell dry weight) of Lactobacillus species was 6.6-35.8%. The values for Lactococcus, Pediococcus and Streptococcus species were 9.0-20.9, 1.1-8.0 and 6.8-17.2, respectively. It was observed that one of the Lactobacillus species did not produce poly-beta-hydroxybutyrate. Generally, Lactobacillus species produced more poly-beta-hydroxybutyrate than the other tested bacteria and no significant correlation was observed between poly-beta-hydroxybutyrate production and cell density of the cultures. (C) 1998 Federation of European Microbiological Societies. Published by Elsevier Science B.V.