In the summer of 1979, a new clinical syndrome in infants less than 10 months of age, characterized by poor appetite, failure to thrive, hypochloremia and varying degree of metabolic alkalosis was described in association with feeding of a chloride deficient formula, Neo-Mull-Soy. More recently, a similar clinical syndrome has been observed in some breast fed infants whose mothers had low chloride concentrations in their breast milk. Seventeen of the original 22 infants enrolled in this study were seen at approximately 42 months of age. Results of our evaluation to date have indicated that the subjects who received the hypochloremic formula continued to have elevations of plasma aldosterone and renin activity levels compared to age matched children and siblings (diet and genetically matched controls). However, at the present time there still is no common clinical characteristic or symptom observed in these infants as a result of the chloride deficient feedings.