OBJECTIVES: Anti-TNF (tumor necrosis factor) drugs are extremely effective for the treatment of many auto-immune diseases such as rheumatoid arthritis, multiple sclerosis, and psoriasis.  The high price of these medications has a significant impact on the Medicaid budget. The objective was to determine the trends in utilization, price and spending for anti-TNF biologics and to analyze the market share competition between biologics. METHODS: A retrospective, descriptive analysis was conducted using national summary files from the Medicaid State Drug Utilization Data from 1998 to 2010. Quarterly number of prescriptions and reimbursement data were calculated for the trends analysis.  Study drugs included all brand and generic names of anti-TNF biologics (e.g., abatacept, adalimumab, anakinra, certolizumab, etanercept, golimumab, infliximab, and rituximab). Market shares for biologics were quantified and compared between 2006 and 2010. The quarterly price per prescription was calculated by dividing the total reimbursement by the total number of prescriptions. RESULTS: The data show an increase in the number of prescriptions reimbursed over time.   Etanercept is the most commonly prescribed biologic in this class, followed by adalimumab.    Medicaid has reimbursed over $1 billion for etanercept, and $500 million for adalimumab.  During the period from 2006Q1 to 2010Q1, etanercept lost 35% of it’s market share.  While all other compounds increased their market share, etanercept lost 40% of its sales market share. All study biologics have experienced an increase reimbursed price since initial market entry after one year of entry into market.  Older biologics like etanercept and adalimumab increased over 100% and 60%, respectively.  Certolizumab which has only been on the market for two years has increased 15%. CONCLUSIONS: Biologic medicines represent some of the most complex but costly products.  It will be critical to devise creative methods and incentives to control the costs of these medicines without stifling the innovation.