The effects of tripchlorolide, an active ingredient (T4) of Tripterygium wilfordii 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 +/- 2.30 vs T4 treated 0.58 +/- 0.47 x 10(-5) mol.L-1) by short-term cultured DSSC of RA patients. The results 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.