Eight of 101 children (8%) seen serially in consultation in an outpatient failure-to-thrive (FTT) clinic had isolated serum bicarbonate (TCO2) levels between 16 and 20 MEQ/dL (normal 22 to 30 MEQ/dL). None of these eight patients had signs or symptoms of renal disease, and all had nonorganic etiologic factors associated with their malnutrition. At the time of this review, follow-up TCO2 measurements were available for seven of the eight children who had attained normal weight (wt/age greater than fifth percentile on National Center for Health Statistics (NCHS) growth chart). All these children had normal TCO2 levels and no evidence of renal disease on follow-up more than 12 months later. Clinicians treating undernourished children who have low TCO2 measurements and have no signs or symptoms of renal disease and identified nonorganic factors, should consider a trial of therapies directed at nonorganic factors. Clinicians should be aware that a high percentage of undernourished children without other medical disease may have abnormal TCO2 measurements that correct after the institution of adequate caloric intake.