Plasma levels of prolyl-hydroxyproline (Pro-Hyp) and hydroxyprolyl-glycine (Hyp-Gly) in healthy volunteers (n = 5) after ingestion of collagen hydrolysate were estimated by liquid chromatography-tandem mass spectrometry. The ratio of Hyp-Gly to Pro-Hyp was distributed in the range of 0.063-0.221. This is a first report for quantification of food-derived Hyp-Gly in human plasma. (C) 2011, The Society for Biotechnology, Japan. All rights reserved.