Sixty-five infants (mean age 14.7 months, range 6-34 months), hospitalized for acute gastroenteritis, were treated with oral rehydration and rapid reintroduction of full feedings appropriate for age. Cow's milk and milk products were eliminated from the diet of 27 infants, whereas the remaining 38 children continued to receive their usual milk and milk products as parts of the mixed diet. There was no difference between the groups in the clinical recovery from diarrhea. No child had prolonged diarrhea. No new cases of clinical atopy were observed at 1-month follow-up, and there were no significant increases in the total or milk-specific IgE levels. Serum IgG and IgA antibodies to beta-lactoglobulin and alpha-casein were initially present in the majority of the children, but there were no appreciable changes in these cow's milk antibodies after gastroenteritis, regardless of the type of diet. It is concluded that cow's milk and milk products can be safely given in acute gastroenteritis as parts of the mixed diet for children over 6 months of age. Rapid reintroduction of feedings is beneficial for recovery from diarrhea, and there appears to be little need for dietary restrictions in this age group.