During 9 months the author observed 309 cases of infection with Salmonella enteritidis, of which 88% were hospital infections in six childrens' wards of three different hospitals. The foci were connected epidemiologically. In 97·7% of those examined, the bacteria were detected in faeces, in 68% in urine and in 27·5% in the upper respiratory tract. Bacteraemia was found in 17·2%. The bacteria were also detected in two air-samples and in two swabs from linen and furniture. All isolated strains were highly resistant to antibiotics and to drying, but sensitive to the action of chloramine. In infected patients with parenteral localization of bacteria, the agglutination test with specific gm antigen was positive in 80% of cases. Many patients were persistent carriers for 5–10 months. In adults a short faecal carrier state was usually observed. The epidemic spread by contact, though in some cases it was probably air-borne. Such epidemics are very difficult to bring to an end.