Determination of catechins in human plasma was carried out by high-performance liquid chromatography with electrochemical detection using a microbore octadecylsilica column. Peak heights for catechins were found to be linearly related to the amount of each catechin injected, from 2 pmol/ml to 2 nmol/ml (r>0.999). Conjugated-form catechins in plasma were hydrolyzed enzymatically using beta-glucuronidase and sulfatase. Catechins in plasma and the hydrolyzed solution were extracted with ethyl acetate and determined by the present method. The time courses of concentrations of catechins in human plasma showed maxima at 1-2 h after ingestion of 340 ml of commercial canned green tea.