Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Targeted inhibition of tumor necrosis factor-alpha (TNF-alpha) is an effective therapy in rheumatoid arthritis (RA). In some rare cases, autoimmune phenomena, including drug-induced lupus and vasculitis, is described. However, the immunological mechanisms underlying the development of autoimmunity are unknown. We report 3 patients that developed autoimmune phenomena while in use of TNF-alpha inhibitor, showing concomitant increase in rheumatoid factor (RF). We hypothesize that the increase in RF several months prior to the occurrence of vasculitis may help identifying other patients at risk for the development of vasculitis secondary to these medications.323815818Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)FAPESP [2008/02917-0, 2009/06049-6]CNPq [300447/2009-4]