The aim of this study is to determine the anaerobic fecal flora of 40 newborn, full-term healthy Turkish babies during I month and to find the difference of the flora depending on the manner of birth. Fecal samples of 15 newborn girls and 25 newborn boys whose mothers had no risk factors like infections and early membrane ruptures were studied. The newborn babies had a weight between 2550 and 4080 g and a gestational age between 38 and 41 weeks. All babies were breast fed and 20 of them were delivered vaginally, 20 by cesarean. Stool samples were taken during 0-2 days, 3-7 days and the 4th week of birth. The isolation of anaerobic bacteria was made from 0.1 dilution of 1 g stool and their identification was confirmed by API 20 A panels. The number of each microorganism isolated from the stool of newborns taken during 0-2 days, 3-7 days and the 4th week of birth was separately evaluated for the group of babies delivered vaginally and for the group of babies delivered by cesarean. The isolation rate of anaerobic bacteria which grew in a high concentration (3+ or 4+) and which showed a significant difference with a P value <0.05 between the two fecal flora of babies delivered either vaginally or by cesarean was considered statistically significant. Peptostreptococcus prevotii, Peptostreptococcus. magnus, Clostridium difficile and Bacteroides capillosus were found only in the fecal flora of newborns, taken during 0-2 days of birth, from babies delivered either vaginally or by cesarean. We have also observed that Peptostreptococcus anaerobius and Bacteroides fragilis were never present in the fecal flora of newborns taken during 0-2 days of birth, Lactobacillus casei and Eubacterium lentum were never present in the fecal flora of newborns taken during 0-2 days and the 3-7 days of birth, and also Bifidobacterium adolescentis were never present in the fecal flora of newborns, taken during the 4th week of birth. We also found, Lactobacillus minutus and Lactobacillus acidophilus only in the fecal flora of newborns taken during 0-2 days and the 4th week of birth from babies delivered vaginally, and also Prevotella bivia in the fecal flora taken during 0-2 days, the 3-7 days and the 4th week of birth from babies delivered either vaginally or by cesarean. The anaerobic fecal flora of Turkish babies is first reported in this study. Since the normal intestinal flora has an important contribution in prevention of systemic infections and also in the maturation of human physiology and immune system, we believe that it is necessary to determine the intestinal flora of babies from different regions which shows differentiation depending on intrinsic and environmental factors. (C) 2002 Elsevier Science Ltd. All rights reserved.