Random urine samples from 614 neonates were screened for metabolites of purine and pyrimidine metabolism using an adapted column chromatographic method. A restricted number of metabolites and a number of unidentified peaks appeared on the chromatograms. No inborn errors of this metabolism were found. The chromatograms were identical in term and in premature or dysmature neonates, except for the presence of more unidentified peaks in the latter group. The pattern was not influenced by the type of feeding or i.v. nutrition. Metabolites of different medications were identified. One female neonate with an increased excretion of uracil was shown to be heterozygous for ornithine carbamyl transferase deficiency.