A method is described for the assay of ascorbic acid in either serum or heparinized plasma. 1. The assay is based on the reduction of ferric chloride by ascorbic acid with the resulting ferrous ion quantitated by the addition of 2,4,6-tripyridyl-s-triazine to form a purple colour with a maximum absorbance at 595 nm. 2. Uric acid interference has been eliminated by the use of a high molarity acetate buffer and by optimising the amount of TPTZ and ferric chloride used. 3. Protein was found to cause rapid fading of the final colour; it was therefore necessary to remove the protein, by addition of 10% trichloroacetic acid, from the specimen prior to the final assay. This had the added advantage of assisting to stabilize the ascorbic acid prior to final assay. 4. All reagents used are easily obtained and no special equipment is required.