This review compares the cost-effectiveness of four biologics - adalimumab (Humira, Abbott Laboratories), anakinra (Kineret, Amgen Inc.), etanercept (Enbrel, Wyeth) and infliximab (Remicade, Schering-Plough) - used in the treatment of rheumatoid arthritis. A decision analytic model was constructed to estimate the costs and effectiveness of these biologics used alone or in combination with methotrexate during 1 year, from the perspective of a managed care organization. The direct costs consisted of drugs and healthcare resources. Effectiveness was measured by quality-adjusted life years based on preference weights and health states in which patients achieved one out of four levels of response according to the American College of Rheumatology (ACR) response criteria (No ACR, ACR20, ACR50 and ACR70), and experienced one of the four levels of adverse events (e.g., no, mild, moderate and severe) due to their treatments. Results were sensitive to changes in treatment costs and probabilities of health states in directions as predicted. For monotherapy and combination therapy regimens, anakinra was the least expensive option while etanercept dominated other treatments.