Community pharmacists are being assigned increased responsibility in assuring the appropriateness and effectiveness of drug therapy. This increased responsibility is reflected in recently passed legislation (OBRA '90) in the United States that requires pharmacists to counsel patients about prescriptions received and to engage in prospective drug use review for Medicaid recipients. The potential impact of this legislation is unclear due to a dearth of research evaluating the effects of community pharmacists' activities on medication use. In addition, there is little research on pharmacists' willingness to assume increased responsibility. Research that would demonstrate the effectiveness of community pharmacists in improving therapeutic outcomes is hampered by problems inherent in conducting experimentally designed research in field settings. This paper examines two issues of concern in such studies--namely, the extent to which those who agree to participate in a demonstration project differ from those who decline to participate and the extent to which differential dropout from treatment and control conditions compromise the comparability of the two groups. Specifically, this report examines pharmacist characteristics related to participation in a demonstration project to improve the care of elderly patients. Community pharmacists in Florida who had earlier been asked to participate in a demonstration project (N = 418) were sent mail questionnaires to assess their attitudinal, demographic and employment characteristics. In particular, researchers were interested in the role orientation of pharmacists in regard to patient counseling and physician consultation, satisfaction with current jobs and career choices, employment settings and treatment vs control group assignment as predictors of participation in the research project. Demographic characteristics were also examined as possible predictors of participation.(ABSTRACT TRUNCATED AT 250 WORDS)