A study of patients with rheumatoid arthritis permitted us to note the interest of tiopronine (sulfhydryl compound of the d-penicillamine type) in the basic treatment of rheumatoid arthritis. The dose of the drug was on average, 1 gram daily, which, in one series of patients, was administered at the start of treatment and in another series, with an increase of dosage of 250 mg every 20 days. The results, judged by the reduction of the Ritchie and Lee index, of the E.R.S. and the steroid and non-steroid anti-inflammatory requirements, are good (very good and good) in 47% of cases. These patients were in an advanced stage of the disease and there had been numerous therapeutic failures. Side effects similar to those observed during treatment with D-penicillamine were present in 38% of cases, and in 31% required stopping treatment. It is likely that the frequency of stopping treatment for side effects was definitely exaggerated. The place of this new drug in the basic treatment of rheumatoid arthritis requires further study by a double blind test with D-penicillamine, and this is at present in progress.