Green tea (Camellia sinensis) catechin profiles in plasma and urine following single dosing and regular ingestion of green tea are not clear. We performed a placebo-controlled intervention study with sixteen healthy volunteers to determine changes in total and free catechins after a single dose and following 1 week of twice-daily green tea. Blood and urine samples were collected before (fasting) and after (60 and 120 min for blood; 90 and 180 min for urine) drinking 200 ml of 1·5 % (w/v) green tea or water (n 8 each), and fasting samples were again collected after 7 d of 150 ml of 1 % (w/v) supplemental green tea or water twice daily. After a 4-week washout, subjects were crossed onto the other treatment and procedures repeated. Plasma results at 1 h post-ingestion showed elevated (P, 0·05) mean epigallocatechin gallate (EGCG; 310 (SD 117) nmol/l; all in free form), epigallocatechin (EGC; 192 (SD 67) nmol/l; 30 % free) and epicatechin gallate (ECG; 134 (SD 51) nmol/l; 75 % free). Fasting plasma after 7 d of regular intake showed increased (P,0·05) EGCG (80 v. 15 nmol/l at baseline) and ECG (120 v. 40 nmol/l), with $ 90 % of both in their conjugated forms. Total EGC was , 10 nmol/l. Post-ingestion conjugation and renal loss of EGC and epicatechin were rapid and high, but were negligible for EGCG and ECG. In the green tea consumed, the content was EGCG . EGC . ECG, and the acute plasma response mirrored this. However, after chronic consumption there was almost no EGC found in fasting plasma, some EGCG was present, but a rather high level of ECG was maintained.Key words: Green tea: Catechins: Polyphenols: Epigallocatechin gallate: Bioavailability: Biotransformation: Antioxidants Green tea (Camellia sinensis) is reported to have various beneficial effects on health (1 -3) . Green tea is rich (35 % of dry weight) in catechins, a family of polyphenolic flavon-3-ols, and these are the putative bioactive agents (2 -4) . The major catechin (about 60 -70 %) in green tea is epigallocatechin gallate (EGCG), but there are also substantial amounts of epigallocatechin (EGC), epicatechin gallate (ECG) and epicatechin (EC) (2 -4) . In vitro studies have demonstrated the powerful antioxidant properties of catechins, particularly EGCG (3 -6) , and human studies have shown that the plasma total antioxidant capacity increases shortly after the ingestion of green tea (3,5,7) . However, poor gastrointestinal absorption, rapid phase II metabolism and urinary excretion of conjugated catechins severely limits their bioavailability and, thereby, their biological effects (4,5,8 -10) . Including the absorption (assessed by their urinary excretion) of ring fission catechin metabolites produced from colonic bacteria increases 'catechin' bioavailability to about 40 % (ranging from ,3 to 100 %), but interindividual differences in urinary concentrations of these metabolites are very large, and their physiological relevance is currently unknown (9 -15) .