We have studied for 1-year period a group of 144 children (31 newborn infants, 62 aged 1 year and 51 aged 2 years) who were randomly selected from the registrar's office of Sevilla with the purpose of determining the incidence of diarrhoea and the prevalence of enteropathogenic microorganisms. Two samples of faeces (one at the beginning and the second by the second semester of the 1-year period) were obtained from all children which were processed for culture and parasite and rotavirus examination. We found a prevalence rate of enteropathogenic Escherichia coli carriers (EPEC) of 7%, of Giardia lamblia of 4% and of rotavirus of 14%. The state of EPEC was more frequent among children from high social-economic status. The state of G. lamblia carrier was six-fold higher in children with body weight alterations and in non-vaccinated or incompletely vaccinated children.