Due to the severe damage caused by free hydroxyl radicals (OH.) to cells and tissues, there is much interest in finding and studying effective and non-toxic OH. scavengers, including traditional Chinese herbs. In this paper, the simple and highly-sensitive technique of capillary zone electrophoresis with amperometric detection (CZE-AD) was used to study the OH. scavenging activities of aqueous extracts from some traditional Chinese herbs. Salicylic acid (SAL) was used as an OH. trap, and the content of OH. could be determined by assaying their products, 2,3-dihydroxybenzoic acid (2,3-DHBA) and 2,5-dihydroxybenzoic acid (2,5-DHBA). The optimum conditions for CZE-AD for the determination of 2,3-DHBA and 2,5-DHBA were explored. The linearity ranges of 2,3-DHBA and 2,5-DHBA were 1.0 x10(-7) approximately 1.0 x10(-4) mol L(-1), and their detection limits were as low as 2 x 10(-8) mol L(-1), which were much better than the CE-UV method often used. The traditional Chinese herbs studied included Radix angelicae sinensis, Rhizoma coptidis, Ligustrum lucidum, Ligusticum wallichii, Radices glycyrrhizae and Semen plantaginis. The experiments showed that the aqueous extracts from all of the above traditional Chinese herds had free OH. scavenging activities, although to different degrees.