A 15 months prospective study of gastroenteritis in hospitalized newborns and infants (N = 201) was combined with a Rotavirus infection surveillance. Stool specimens were investigated weekly (CFT). From patients with gastroenteritis (N = 320) an infectious agent could be detected on average in 41% of each patient group: Rotavirus N = 54, Staph. aureus N = 22, toxin producing E. coli N = 4, other bacteria N = 25, Candida albicans N = 17, Echovirus 11 N = 1. With certain exceptions, the pathogens were distributed equally within the patient groups. However, Candida albicans appeared most frequently in premature children and the highest incidence of Rotavirus infections was observed in premature small for date babies. Rotavirus caused the mildest illness. The severest forms had usually no detectable cause. Bacteria took up an intermediate position. 68% of patients with detectable Rotavirus in the faeces had symptoms. However, treatment was required in only 25% of premature and small for date babies and 40% of normal newborns. In newborns and infants an isolated tachypnoea was observed 3 days prior to onset of a Rotavirus induced gastroenteritis. Breast fed infants showed no evidence of increased protection. Rotavirus antibodies were detectable in 58% of children prior to infection. The study presents evidence for the value of separate of patient care and meticulous hand disinfection, especially in the case of Rotavirus induced gastroenteritis.