Many of the adverse reactions produced by penicillamine and other compounds with an active sulfhydryl group form a distinctive pattern when viewed as a class. Alterations in taste perception, mucocutaneous lesions, proteinuria due to immune-complex membranous glomerulopathy, and pemphigus are adverse reactions that have been encountered with all of the compounds discussed herein. Hematologic reactions such as neutropenia and thrombocytopenia occur rarely and with variable frequency. The angiotension converting enzyme inhibitor captopril has an active sulfhydryl group. When it was first given in high doses to patients with severe hypertension, adverse effects similar in pattern to those just outlined were reported. With reduced doses and more careful patient selection, the more serious reactions are no longer found, but disturbances of taste perception, rash, and oral mucosal ulcers are still encountered.