This paper describes two children with diarrhea, hypokalemia, and VIP-secreting ganglioneuroblastomas, and includes further evidence that VIP is the cause of the loose stools among patients with such tumors. It suggests that the level of this peptide should be measured in pediatric patients with intractable diarrhea of unknown etiology. Clinicians have long recognized intractable diarrhea as an occasional feature of neuroblastoma, ganglioneuroblastoma or ganglioneuroma. Until recently catecholamine was thought to cause the frequent stools in some patients with these tumors. New radioimmunoassay methods, the identification of new hormones and hormone-like substances, and the discovery that some of the tumors which cause diarrhea secrete Vasoactive Intestinal Peptide (VIP), make it probable that this substance is responsible for the diarrhea in such patients.