The lack of environmental sanitation measures is a worldwide problem, especially in developing countries, and greatly facilitates the spread of disease. This thesis aims to contribute towards a better understanding of the effect on diarrhoea, nutritional status and intestinal nematode infections of drainage and sewerage in an impoverished urban environment. After an extensive literature review of some relevant aspects of the health impact of environmental sanitation, field research was designed and conducted in nine poor urban areas of the city of Salvador (pop. approximately 2.3 million), capital of Bahia State, in northeast Brazil. The study was targeted to a sample of children under 15 years old living in the poor urban areas of the city at the time of the field work (August 1989-November 1990). An extensive questionnaire was applied to collect information on each child and on the conditions of the family and the household, three stool examinations of the children 5-14 years old were performed (to measure nematode infection and reinfection), diarrhoea was monitored fortnightly, in children under 5 years old for one year, and anthropometric measurements taken every two months. The results showed that among children in neighbourhoods with unimproved community sanitation the incidence of diarrhoea was consistently higher and the nutritional status, expressed by the mean height-for-age z-score, was significantly lower throughout the study period as compared to those with improved sanitation. Regarding intestinal nematode infections, as the level of community sanitation improves, the following trends were noted: prevalence and intensity of infection and reinfection declined, risk factors for infection became more numerous and more significant, clustering of cases by house­ hold became more significant, predisposition of individuals to reinfection and to heavy infection became more marked, and infections with different species were increasingly aggregated in the same individuals. These results suggest that sewerage and drainage can have a significant effect on diarrhoea, nutritional status and intestinal nematode infections and that the evidence of the health impact was strongest for intestinal nematode infections. The interpretation of these epidemiological findings in the light of the Brazilian health, urban and social policies contributes to a comprehensive framework for the control of nematode infections, diarrhoea and malnutrition in poor urban areas of Salvador and elsewhere.