2 mercapto propionyl glycine (tiopronine) has, like D-penicillamine, a thiol radicle; it is a powerful chelating agent of heavy metals. This analogy suggests that it may be used in rheumatoid arthritis. A preliminary double blind study lasting four months comparing 1g./day in 20 patients and a placebo in 10 patients showed slight (non significant) efficacy concerning all parameters. An open study using 1.5 g. daily is being carried out in 32 patients, and we note a beneficial effect on the morning stiffness, the joint index, the functional index, the prehension strength, the E.S.R., and the joint swelling. The side effects are similar to those of D-penicillamine: loss of taste, proteinuria, mucous ulceration, which required stopping treatment. The therapeutic effect within 4 months and was maintained for 18 months in the 15 patients under treatment. A new double blind trial comparing placebo and tiopronine at a dose of 1.5 g. daily is in progress.