PROBENECID (Benemid) * resulted from a prolonged research effort directed toward the discovery of a safe agent that, administered orally, would physiologically inhibit the renal tubular secretion of penicillin.1Introduced into clinical medicine on July 22, 1949,2the use for which it was intended has increased steadily, and new indications for the drug have been disclosed. A conservative estimate indicates that 4,000,000 patient days (15,626 patient years) of therapy have been administered. Granting that the record of side-effects following the use of any therapeutic agent is not static, and that continuing use will bring to light an increasing number of side-effects and toxic manifestations, an appraisal from time to time seems appropriate. A preliminary assessment of the toxicity of probenecid was presented in 1951 on the basis of 701 patients,49and it is now possible to report on 2,502 patients. The information reported here has been derived from