(1) An account of five cases of gastro-enteritis is presented in a preliminary report of an investigation which is being undertaken at the National Children’s Hospital, Dublin. (2) Four of the cases were of the acute enteral type and one of the acute parenteral (i.e., otitis media). (3) A method of continuous intravenous drip therapy is described and its advantages and difficulties discussed. (4) A method of ascertaining the serum density is briefly described. (5) The results obtained in these and other cases suggest that the intravenous method is often life-saving in cases of extreme dehydration. (6) A further detailed report will be published later.