To understand the relationship between tea consumption and its biological effects, plasma and tissue levels of (-)-epigallocatechin-3-gallate (EGCG), (-)-epigallocatechin (EGC), and (-)-epicatechin (EC) were measured after rats and mice were given a 0.6% green tea polyphenol preparation as the drinking fluid for different periods of time. EGC and EC levels in rat plasma increased over time and reached peak values (3 times the Day 1 values) on Day 14. Then the plasma levels of tea catechins decreased, to Day 1 values on Day 28. The plasma concentrations of EGCG were much lower than those of EGC or EC. High levels of EGC and EC were found in urine, whereas high levels of EGCG were found in feces. The changes in the urinary and fecal excretions of tea catechins could not account for the above-described changes in the plasma levels. The amounts of catechins in different tissues reflected the ingestion, absorption, and excretion pattern. When the green tea polyphenol preparation was given to mice, the "increase-and-then-decrease" pattern of catechin levels was also observed in the plasma, lung, and liver; the EGCG levels were much higher than in the rats. The results suggest that consumption of tea by rodents could induce adaptive responses affecting blood and tissue levels of tea catechins with time and that investigation of a similar phenomenon in humans is warranted.