Consumers may face prescription choices in three-tier plans, primarily between lower-cost generic drugs, formulary (tier 2) brands, and higher-cost nonformulary (tier 3) brands. To determine if consumers' beliefs about medications influence their prescription choices, a preliminary evaluation of the effect of such beliefs on prescription purchasing behavior was conducted in an MCO population. Attitudes about prescription drug coverage and perceptions regarding medications had no demonstrated effect on formulary compliance or rates of discontinuation of nonformulary medications. The findings appear to support the concept of three-tier plans, and increasing copayments seems to facilitate greater adherence to health plan formularies.