Infliximab, a chimeric monoclonal antibody to tumour necrosis factor-alpha, contains murine protein elements and targets the immune system, raising concerns about the potential for immune sensitization and immunosuppressive sequelae. However, long-standing inflammatory disease with high activity and chronic immunosuppressant therapy can also predispose patients to immunosuppressive sequelae. Patients with Crohn's disease, rheumatoid arthritis and other indications received single or multiple doses of infliximab and their condition was followed for up to 3 years. Adverse events, most frequently headache, nausea, and upper respiratory tract infection, were generally mild and occurred in 76% of infliximab-treated patients vs. 57% of placebo-treated recipients. Human antichimeric antibodies developed in 13% of patients, increasing the potential for subsequent infusion reactions. Antibodies to double-stranded DNA developed in a small percentage of patients. Other antinuclear antibodies characteristic of serum lupus erythematosus were not found; no patient developed a true lupus syndrome and no other autoimmune disorders were reported. Infliximab is not associated with typical immunosuppressive sequelae, such as infections and malignancy, or with autoimmune disorders. Infliximab therapy was well tolerated, serious adverse events were infrequent, successfully managed with medication and without sequelae, and overall mortality was within the expected incidence for this patient population.