Forty-eight children below 18 months of age suffering from acute gastroenteritis were given a glucose-electrolyte mixture (GEM) for the first 24 h following hospital admission. They were then allocated alternately to the study group which immediately went back to full-strength cow's milk feeds, or to the control group to which milk was reintroduced gradually over a 4-day period. The majority of infants in both groups had an uncomplicated recovery (70 and 96%, respectively). A complicated recovery, however, occurred more commonly in the study group. Seven patients in this group, compared with only one in the control group, had an immediate recurrence of symptoms of such severity that a return to intravenous fluids or the GEM was necessary. These complications were confined to those less than 9 months of age. It is concluded that children over 9 months of age with acute gastroenteritis may be given full-strength milk immediately after 24 h of treatment with a glucose-electrolyte solution, but for children under 9 months the conventional regrading over several days should be retained.