The purpose of this study was to determine whether the methylation of nicotinamide to N-methylnicotinamide could discriminate between differences in methionine nutritional status, and by implication methylation capacity, in healthy humans. As part of this thesis, a highly selective high performance liquid chromatography (HPLC) method for the determination of N-methylnicotinamide (NMN) in urine and plasma was developed and validated. Quantification was by fluorescence detection of the 1,6-naphthyridine derivatives, formed after incubation of NMN with acetophenone in alkaline conditions. Seven volunteers participated in a trial to evaluate the ability of a nicotinamide load test to discriminate between changes in the methylation status of the individual. The methylation status was measured as the time dependent changes in plasma NMN concentrations after a nicotinamide load. A basal nicotinamide load test was performed on each individual. The methylation status was then changed, by means of a methionine load, and the nicotinamide load test was repeated during the enhanced methylation state. The dynamic changes in N-methylnicotinamide levels indicated that the methionine load changed neither the plasma NMN concentrations, nor the rates of NMN formation. The conclusion of this study was that nicotinamide loading could not be used as a dynamic function test to assess biological methylation in healthy humans. / Dissertation (MSc (Chemical Pathology))--University of Pretoria, 2006. / Chemical Pathology / unrestricted