A brief review of data on the measurement of ascorbic acid in biological samples is the subject of this paper. Data on the metabolism, biological functions, preferable biological materials (serum/plasma), reference intervals, preanalytical variables, storage conditions, analytical performance characteristics, calibration, quality control, interlaboratory comparability are presented. Evidence based data on the following aspects are presented: – suitability of serum/plasma for the measurement in monitored persons, – stabilization of ascorbic acid by adding metaphosphate, – selection of selective chromatographic, enzymatic and electrophoretic methods of measurement. We found controversies in data on the relationship between ascorbic and dehydroascor bic acid in serum/plasma and as well for the mechanism of dehydroascorbic acid origin in serum/plasma. The question whether we assess ascorbic acid or the sum of ascorbic and dehydroascorbic acid remains open.

        Key words: vitamin C, serum/plasma, stability, methods of assessment, interlaboratory comparability.