During 1978-1979, more than 20,000 infants may have been exposed to chloride-deficient formula (CDF). A number of these children were noted to suffer from severe metabolic alterations, principally hypochloremic metabolic alkalosis (HMA). The present study examined 21 children who were exposed to CDF and developed HMA. Pediatric records were reviewed, medical and feeding histories were obtained from the parents, and children were administered the Bayley Scales of Infant Development (BSID). The range of age at testing was 13 to 29 months (mean=23.2). The Bayley Mental Development Index (MDI) ranged from 67 to 127 (mean=98.5) Length of exclusive use of CDF without supplementation with solids or other milk/formula (LENEXC) had a significant negative correlation with MDI (r=-.55, p=.01). When length of exclusive use of CDF, age of onset of CDF use and age at testing were entered into a multiple regression analysis, LENEXC remained associated with MDI (R2=.39, p<.05). Sixteen of these children were re-examined at ages ranging from 40 to 51 months (mean=43.8) using the McCarthy Scales of Children's Abilities. There was a significant negative correlation between LENEXC and the perceptual-performance scale (r=-.51, p<.05) and between LENEXC and the motor scale (r=-.52, p<.05). These data raise concern about the long-term outcome of these children.