Various enzyme defects in the metabolic pathways of purines and pyrimidines are known, which result in different diseases occurring in children. They mainly affect kidney function, central nervous system, immunological and blood system. For example, complete deficiency of HPRT (hypoxanthine-guanine-phosphoribosyl-transferase) causes the Lesch Nyhan syndrome, which is characterized by hyperuricemia, mental retardation, choreoathetosis and compulsive self-mutilation. XDH deficiency (xanthine-dehydrogenase) causes in arthropathia and myopathia. For screening for these and other enzyme defects, urinary purine and pyrimidine excretion is considered a simple diagnostic tool. The purpose of the present study was to establish a reverse phase HPLC screening method for urinary purines and pyrimidines and to establish age related reference ranges in children for the urinary excretion of orotic acid, uracile, pseudouridine, uric acid, hypoxanthine, xanthine, thymine, 7-methylguanine, inosine, guanosine and adenosine.