OBJECTIVES: Managed care companies implemented step therapy (ST) policies to reduce utilization of infused biologics in new patients.  The purpose of this analysis was to compare market shares for biologic products for plans identified with ST policies versus all other claims (Other) in a large US administrative database.  METHODS: Data from all plans with a ST policy throughout 2010 were compared to all other biologic claims during the same time period using data from the Wolters Kluwer Prometis® and Medical databases.  Available data included payer, prescription (Rx), diagnosis (Dx) and procedure (Px) claims with unique anonymised patient identifiers. For 2010, biologic claims were evaluated based on: patients with Rx data having at least one biologic prescription and patients with Rx and Px data, for the subset with ≥ 1 Rx claim (any type) and  ≥ 1 medical claim (all cause). The number and percentage of patients receiving a biologic in 2010, was described.  A secondary analysis of only subcutaneous (SC) products in the Rx database was conducted.  RESULTS: Sixteen different plans had a ST policy in 2010.  There were 280,271 patients (5,960 ST and 275,927 Other) with at least one biologic in the Rx claims, 274,495 with at least one claim in the Rx and Px combined data (7,936 ST and 266,559 Other), and 271,635 with claims for SC biologics in the Rx data (5,853 ST and 267,379 Other).   There was less than a 4.6% difference in patient market share within any individual products, when comparing market shares of products within ST policies vs Other policies.  These results were consistent for all Rx, Rx and Px, and for the Rx only cohort, including when restricted to only SC products. CONCLUSIONS: Policies designed to reduce overall patient proportions using infusion biologics suggest only a very modest effect in this population-level comparison.