Several hydroxyproline (Hyp)-containing food-derived collagen peptides were identified in human blood after oral ingestion of gelatin hydrolysates. However, these types of peptides were not quantified in human plasma. In this report, a sensitive LC-MS/MS method was introduced for simultaneous quantitative analysis of Hyp-containing peptides. All peptide concentrations were determined accurately, with all coefficients of determination (r(2)) >0.999. The method achieved detection and quantification limits of 0.01 pmol/ml and 12.5-1,000 pmol/ml in plasma, respectively. Concentrations were quantified for nine Hyp-containing peptides in human plasma by this method, identifying Pro-Hyp (C(max) = 60.65 +/- 5.74 nmol/ml) as the major constituent of food-derived collagen peptides, while the minor components were Ala-Hyp-Gly, Ser-Hyp-Gly, Ala-Hyp, Phe-Hyp, Leu-Hyp, Ile-Hyp, Gly-Pro-Hyp, and Pro-Hyp-Gly (C(max) from 23.84 to 0.67 nmol/ml). Thus a total of nine Hyp-containing peptides in human plasma were successfully quantified by this approach. The concentration of Hyp-containing peptides is substantially higher than that following oral administration of other peptides.