Prognosis of several autoimmune diseases, especially rheumatoid arthritis (RA), ankylosing spondylitis, Crohn's disease (CD), and psoriasis, usually refractory to conventional treatment improved considerably with the introduction of tumor necrosis factor alpha (TNF-alpha) antagonistic agents, which is now available (infliximab, etanercept, and adalimumab). However, a portion of patients persists with active disease, infusion reactions, and relapses even during current biological therapy. One of the reasons for this is the associated immunogenicity to these drugs. The incentive for induction of antibodies against anti-TNF-alpha agent depends mainly on its constitution. Chimerical drugs have a higher capacity of inducing immunogenicity compared to completely human drugs. Among the three anti-TNF-alpha agents, this phenomenon has been studied mainly in patients using infliximab, especially in RA and CD. The prevalence of anti-infliximab antibodies in RA varies from 12% to 44% and seems to be inversely proportional to the level of seric infliximab and therapeutic response. The use of etanercept was associated to the development of anti-etanercept antibodies in 0% to 18% of patients, without apparent effect on effectiveness or adverse events. Studies with RA and CD patients show prevalence of anti-adalimumab antibodies from 1% to 87%. Immunosuppressive drug addiction can reduce the induction of anti-TNF-alpha antibodies.