Children of three different age groups (1 to 6 months, 13 to 24 months and 26 to 47 months of age at beginning of survey) were studied weekly for their intestinal fauna for a period of 16 weeks. The intestinal fauna of the youngest group were limited quantitatively and qualitatively and only flagellate protozoans were detected. Stool examinations of children 13 to 24 months of age indicated that the period of 15 to 20 months was very important from the standpoint of general establishment of intestinal fauna in a child. Flagellates increased in number, amebas were detected and the eggs of Ascaris, Enterobius and Hymenolepis nana were passed with feces. At the age of 16 to 18 months Entamoebs histolytica became established, the rate of infection increasing rapidly the following 2 years. In the oldest age group protozoan and helminth populations increased markedly and none of the 28 children escaped invasion by intestinal fauna. A total of nine species of protozoa, plus both the large and small races of E. histolytica and six different helminths were found in the latter age group by the time this study terminated. Although the village of Sindbis lies in an endemic area, neither of the two schistosomes common to Egypt were found.