SUMMARY: Four hundred and fifty-two strains of lactobacilli, including representatives of all recognized species and 197 freshly isolated cultures, were studied. It was possible to classify 390 (86·3%) of these into eight groups on the basis of the results of six physiological tests. The tests used were the production of gas from glucose and citrate, and of ammonia from arginine, growth at 15, 45 and 48°, heat survival at 60 and 65° and tolerance of 4, 6 and 8% (w/v) sodium chloride.