Abstract: The effects of tripchlorolide ,an active ingredient(T₄)of Tripterygium uilfordii Hook on the production of prostaglandin E₂(PGE₂)by synovial cells of rheumatoid arthritis(RA)patients were investigated.Six cases of definite RA(female 5,male 1,mean age 45 with an average course of disease of 9 years )were selected.Surgically obtained synovium specimen were dissociated into digested synovial single cells(DSSC). The cells were incubated with various concentrations of T₄ for 48 hours.Using radioimmunoassay T₄ was found to significantly inhibit the production of PGE2(control 6.10±2.30vs T₄ treated 0.58±0.17×10^-5 mol·L^-1) by short-term cultured DSSC of RA patients. The result of this study suggests that T₄ may be useful in the forthcoming treatment of RA due to its inhibition of production of PGE₂ by synovial cells.