Physiochemical characteristics and flora of diarrhoeal and recovery faeces were investigated in 14 Kenyan children with acute gastro-enteritis. Causative micro-organisms were Shigella, Campylobacter, enterotoxigenic Escherichia coli, rotavirus and unknown in 6, 2, 1, 2 and 3 patients, respectively. The mean values of the pH of the diarrhoeal specimens were significantly higher than those of the recovery specimens. Large amounts of acetic acid and many other kinds of fatty acids were detected in the recovery specimens, but small amounts and few kinds of fatty acids were detected in the diarrhoeal specimens. Bacterial counts of anaerobic organisms, such as Bacteroides, Bifidobacterium, Lactobacillus and Eubacterium, were lower in the diarrhoeal specimens than in the recovery ones. The normal anaerobic intestinal flora is remarkably disturbed in patients with acute gastro-enteritis. This may result in changes in fatty acid contents and in the pH of diarrhoeal faeces.