The aerobic gram-negative faecal flora of 78 reptiles consisting of 46 species (39 lizards of 23 species, 15 tortoises of 9 species, 24 snakes of 14 species) was studied. Salmonella was found to be present in 50% of lizards, in 16% of tortoises and in 16% of snakes. There were all together 15 different serotypes. Edwardsiella tarda was isolated in 20% of tortoises, in 12% of snakes but only in 3% of lizards. Tortoises represent therefore the possible normal habitat of Edwardsiella tarda. We isolated Arizona specially from snakes as was described by many authors. A new serotype (Arizona 26a, 26b:27 - 21 = S. arizonae 61:Z10:Z35) was found in a rattlesnake. There were found also much amounts of Citrobacter (52%), E. coli (50%), Proteus mirabilis (49%), Proteus morganii (18%), Proteus rettgeri (26%), Proteus vulgaris (32%). Klebsiella and Enterobacter seem to prefere the lizards. The overwhelming majority of the studied bacteria were lactose-negative, corresponding to the inability of reptiles producing lactose. The normal habitat of Salmonellae in reptiles and the high phylogenetic age of reptiles allows the hypothesis that salmonellae could have a similar old age as their host animals, because the ecological niche, i.e. the bowel of reptiles, has no changed for some hundred million years.