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Summary:The continuous spectröphotometric assay of 5'-nucleotidase originally described by Heinz et al. ((1980) J. Clin. Chem. Clin. Biochem. 18, 781-788) was modified and fully automated on a Kem-O-Mat transfer analyzer, using inosine S'-monophosphate äs Substrate. The reaction product was hydrogen peroxide and the redüction of NADP was observed for 10 minutes at 340 nm and at a reaction temperature of 30 °C. The different factors involved in the enzyme reaction were checked, including the Substrate concentration, reaction rate, linearity and Substrate preservatiort. Normal values ranged from l to 13 U/1. Between-day reproducibility was estimated with two different commercial control serä, and the coefficient of Variation was 5% for the upper limit of normal activity (23 U/l). There was good agreement between the present method and a semi-automätic colorimetric technique (for 100 sera tested by both methods, the correlation coefficient was 0.974 and the regression line equation, y = 0.85 x-1.5). Despite the lengthy reagent mixture preparation procedure, the method permitted assay of 50 samples per hour. The occurrence of high serum blanks in certain pathological states is discussed. Kontinuierliche Bestimmung der katalytischen Aktivität von 5'±Nucleotidase im Serum mit Inosin-5'-monophosphat als Substrat und völliger Mechanisierung mit einem Transfer-Analyser (Kem-O-Mat) Zusammenfassung