OBJECTIVES: The purpose of this study was to evaluate the impact of specialty pharmacy prior authorization (SPA) program on prescription costs for the biologic response modifiers (Amevive, Enbrel, Humira, Kineret, Raptiva, and Remicade)—a new class of medication for the treatment of several disease states such as Rheumatoid Arthritis. METHODS: Prescription data were obtained from a pharmacy benefit manager's pharmacy claims database. This study used a retrospective case-control one-to-one matching approach based on patient age, gender, and client characteristics including the number of eligible members, client type and region. The case clients had enrolled in the SPA program in January 2005 and had remained part of the program by December 31, 2005. Clients whose members did not use the biologic response modifiers were excluded from the study. Per eligible member per month (PMPM) total costs was the outcome measured. RESULTS: The average PMPM total, plan and member costs were $1.33, $1.30, and $0.03 in the case group, while the average PMPM total, plan and member costs were $1.51, $1.47 and $0.04 in the control group. Clients who implemented a specialty pharmacy prior authorization program for the biologic response modifiers saved an estimated PMPM total cost of $0.18. CONCLUSION: Implementing a specialty pharmacy prior authorization program reduced prescription drug costs for the biologic response modifiers.