The development of autoimmune diseases in some patients treated with D-penicillamine (DPA) suggests that the reported occurrence of a conduction disorder at the neuromuscular junction and the development of a reversible myasthenia gravis in rheumatoid disease, progressive systemic sclerosis or Wilson's disease after the use of DPA are part of a general predisposition for autoimmune disease related to DPA therapy. The case reported is an example. The DPA- induced myasthenia gravis (MO) is similar to the spontaneous MG clinically and electrophysiologically, though ocular signs prevail in the former. Antibodies to acetylcholine receptor have been demonstrated and thymic hyperplasia also has been formed. Regarding the onset of myasthenic manifestations the duration of the treatment with DPA varies from 6 to 10 months. The action of DPA on the neuromuscular junction is different from that occurring in spontaneous MG. The pathogenesis of the DPA induced MG is still obscure. The chemical properties of DPA permit it to react with many proteins and some alteration of proteins may appear, with structural changes in the composition and antigenicity of the collagen fibers. In vitro DPA causes disorder of acetylcholine receptor bridges to a,b,g sub-units with reduction of the S-S bridges in the g-subunit. This decreases the linkage of high affinity and abolishes its positive cooperative system, reducing the S-S connection in the a-unit near the acetylcholine linkage. The interation between DPA and receptor may induce antigenic alteration in this latter, starting the autoimmune phenomena. The other possibility is the stimulation of prostaglandin E-l synthesis by DPA may fill the allosteric place of ACh receptor, interfering on the neuromuscular junction.