SummaryExcretion patterns of pyrimidines and purines in patients with various types of hyperammonemia have been investigated by a-dimensional thin-layer chromatography and high pressure liquid chromatography (HPLC). For the quantitative analysis of pseudouridine, uracil and uridine a new procedure has been developed, consisting of pre-fractionation with Dowex 1 X 8, followed by dual column HPLC on a strong anion-exchanger and a reverse phase column. Thymine has also been analyzed in the pre-fractionated urine by a new HPLC method using the reverse phase column in combination with a strong cationexchange column. Quantitative data for urinary pyrimidines and uric acid in hyperammonemia are given. In patients with a defect in one of the urea cycle enzymes, the level of pyrimidine excretion was found to depend on plasma ammonia concentrations.In other hyperammonemic patients, an increased excretion of erotic acid, uracil and uridine has only been found in one of the two pati'ents with lysinuric protein intolerance, all other patients showing normal excretion patterns, Elevated uric acid excretions have been found frequently in our patients with hyper~monemia, but they did not always coincide with high plasma ammonia levels. A possible explanation for the difference in the excretion levels of the various pyrimidines is discussed.

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SUMMARYChromatographic characteristics of urinary metabolites of theophylline were studied by two-dimensional thin-layer chromatography, high-performance liquid chromatography and gas chromatography-mass spectrometry. Quantitative data for the urinary metabolites of theophylline in asthmatic children are given. It was shown that 1,3-dimethyluric acid is the predominant excretory product. In addition, smaller amounts of 1-methyluric acid, 3-methylxanthine and unchanged theophylline were found. Excretory patterns after theophylline ingestion before and during the administration of allopurinol in asthma patients and in rats suggest the existence of three metabolic pathways of theophylline. The administration of this drug to a patient with xanthine oxidase deficiency resulted in the excretion of 1-methyluric acid in addition to 1,3-dimethyluric acid, 3_methylxanthine, 1-methylxanthine and unchanged theophylline. It was concluded that in man the oxidation of theophylline is not catalysed by xanthine cxidase;