Free radicals are involved in the pathogenesis of Rheumatoid arthritis, a systemic autoimmune disorder characterized by unchecked synovial infl ammation. Allylpyrocatechol, a   phytoconstituent of Piper betle leaves, has potent anti-infl amatory activity and this study evaluated its anti-oxidant effect on the synovial infi ltrate of patients with Rheumatoid arthritis. The ex vivo effect of allylpyrocatechol upon generation of reactive oxygen species in neutrophils, macrophages and lymphocytes was measured by fl ow cytometry using dichlorodihydrofl uorescein diacetate, wherein it signifi cantly decreased basal levels as also scavenged phorbol myristate acetate generated reactive oxygen species. Furthermore, its effect on generation of superoxide and hydroxyl radicals produced within infi ltrated neutrophils was measured by cytochrome c and deoxyribose assay, respectively. Allylpyrocatechol signifi cantly scavenged superoxide and hydroxyl radicals in infi ltrated neutrophils. The effect of allylpyrocatechol on nitric oxide was measured in macrophages using 4,5-diaminofl uorescein diacetate by flow cytometry wherein it decreased production of nitric oxide in infiltrated macrophages, which correlated with its in vitro nitric oxide scavenging activity. Taken together, this ex vivo study has established that allylpyrocatechol has potent scavenging activity and could be considered as an add-on therapy in the treatment of infl ammation-associated disorders like Rheumatoid Arthritis.