D-penicillamine is rapidly absorbed from the intestine and appears in plasma as free penicillamine, cysteine-penicillamine disulfide, and penicillamine disulfide. Penicillamine binds firmly to serum and tissue proteins. The urinary excretion of S-methyl-D-penicillamine, cysteine-penicillamine disulfide, penicillamine disulfide, and a newly identified metabolite, homocysteine-penicillamine disulfide, has been quantitated for patients with rheumatoid arthritis, cystinuria, and Wilson's disease. Fifty percent of an oral dose is excreted in the feces, but the metabolites have not yet been fully characterized. The pharmacologic effects of D-penicillamine are associated with disulfide bond formation or cleavage, thiazolidine formation, and metal chelation.