Several strains of Lactococcus lactis subsp. lactis, Lactobacillus casei and Lactobacillus plantarum isolated from traditional goats' cheese have been studied for titratable acidity, proteolysis in milk and enzymic activities. Aminopeptidasc activities were measured with whole cells and cells permeabilized with Triton X-100. Caseinolytic activity was investigated using electrophoresis in polyacrylamide gel with sodium dodecyl sulphate. Lc. lactis subsp. lactis had a level of proteolytic activity in skim milk greater than that of Lb. casei, while this activity in Lb. plantarum was very low. Alanine aminopeptidase activity was almost non-existent for all strains tested, while lysine aminopeptidase activity appeared to be of fundamentally intracellular origin. Leucine aminopeptidase activity was also greater in cells that had been permeabilized than in whole cells for Lb. casei and Lb. plantarum. Lc. lactis subsp. lactis leucine aminopeptidase activity was greater in whole cells. No significant hydrolysis of casein was found with Lb. casei I FPL 725 and Lb. plantarum IFPL 722 permeabilized with Triton X-100 after 24 h incubation with whole bovine casein.