Tetrahydrocurcumin (THC), one of the major metabolites of curcumin, exhibits many of the same physiologic and pharmacological activities as curcumin and in some systems may exert greater antioxidant activity than curcumin. However, evaluation of clinical efficacy is limited by lack of sensitive methods for quantifying intake/absorption in blood or urine. We have developed a sensitive high performance liquid chromatography (HPLC) analytical method for detection of THC in plasma and urine. The method involves extracting the THC from 0.2 mL samples with 95% ethyl acetate/5% methanol, and beta-17-estradiol acetate as an internal standard. Analysis with a reversed-phase C18 column and UV detection at 280 nm demonstrates linear performance from 0.050 to 6.0 microg/mL in plasma, and 0.060 to 6.0 microg/mL in urine. The coefficients of variation for intra- and inter-assays were each<8.6%. The average recovery of THC from plasma and urine was greater than 98.5%. These data demonstrate a rapid, sensitive and accurate method for HPLC quantification of THC in plasma and urine.