The B7 family of molecules on antigen presenting cells (APCs) regulate T cell activation. They deliver stimulatory signals through CD28 and inhibitory signals through CD152, or cytotoxic T lymphocyte-associated antigen-4 (CTLA-4). CTLA4Ig (abatacept) is a soluble chimeric protein consisting of the extracellular domain of human CD152 linked to the modified Fc portion of human IgG1. By binding to B7-1 (CD80) and B7-2 (CD86) molecules on APCs, CTLA4Ig blocks the CD28-mediated costimulatory signal for T cell activation. Success with abatacept has been noted in psoriasis. Abatacept was administered to two patients with refractory psoriasis and psoriatic arthritis after the patients had failed all conventional treatment methods. Both patients experienced very brief improvement in disease. The improvement, however, was not continued, and both patients were taken off the medication. The small patient population limits the extrapolation of the present authors' results to the larger population. Furthermore, the present authors' patients have very severe, refractory disease and do not adequately represent the majority of psoriasis patients. Although the present authors' patients demonstrated brief response to drug, this response was not sustained. No adverse events were reported in the present authors' patients.