Approximately 25% of reported cases of salmonellosis are in children < 4 years of age. Our previous investigations have been unable to identify the major risk factors for the development of disease in this age group. The purpose of this study was to evaluate the role of the home environment in the development of salmonellosis in children < 4 years of age. Contact was made with the family of children < 4 years of age who had Salmonella isolated from a specimen submitted to the clinical microbiology laboratory. A questionnaire was administered concerning food preparation and consumption, formula preparation and consumption, parental occupation, day care attendance, water source, and other environmental factors. An investigation of the home was carried out in an attempt to culture all occupants, pets, food preparation and storage areas, left-over foods, and other miscellaneous sources. Isolates from the home with a serotype identical to the original patient isolate underwent DNA fingerprinting by pulsed-field gel electrophoresis. DNA patterns were inspected for similarities. Home inspections were carried out in 66% of eligible homes on the average of 3.4 days (range: 0-11 days) after the confirmation of the Salmonella isolate. Five hundred and twenty-nine cultures from 50 homes were obtained: foods (123), household members (73), refrigerator(52), water (47), counter top (46), soil (42), can opener (36), vacuum cleaner(34), animals/pets/insects (26), others (50). Sixteen households had the identical serotype with the identical DNA fingerprint of the index patient, three of these have also included a second serotype, and three households had an enitrely different serotype. The identical serotype was found in multiple locations (4), dirt surrounding the front door (4), household members (3), vacuum cleaner (2), pet (2), and refrigerator shelf (1) in these households. Only 31% of other persons in the households allowed testing but nine households had other persons with positive cultures. Four of the households had individuals develop illness prior to the development of disease in the index patient, one household had a individual who became ill after the index case and four households had individuals with positive cultures who were asymptomatic. These data illustrate the importance of the child's environment in the development of salmonellosis. Parents should be educated about the importance of the home environment in the development of disease with Salmonella.