To determine the range of normal values, we studied urinary excretion of oxalate and glycolate prospectively and longitudinally in a cohort of 30 healthy term infants. Random urine samples were obtained at 2 days, 2 weeks, and 2, 4, 6, and 9 months of age. The results had a log-normal distribution. The mean oxalate/creatinine ratio, as determined by the oxalate oxidase method, was 0.08 (in milligrams of oxalate to milligrams of creatinine) with a normalized range of 0.02 to 0.31. The mean ratio when oxalates were measured by using the Olthuis assay was 0.13 (range 0.03 to 0.53). The mean glycolate/creatinine ratio was 0.07 (range 0.02 to 0.26). These values did not correlate with increasing age. The oxalate/creatinine ratios were higher in formula-fed infants than in those who were fed human milk (0.14 +/- 0.16 vs 0.08 +/- 0.04; p < 0.01).