OBJECTIVE: To assess factors associated with participation in pharmaceutical care and the benefits of participation--in terms of amount of information about medications, administration of medications, and awareness of side effects. DESIGN: Quasi-experimental design, with a control group. Medication Survey, administered 6 months after pharmaceutical care intervention to participants, refusers, and controls. Logistic regression analyses. SETTING: Three staff clinic pharmacies and three contract clinic pharmacies affiliated with a health maintenance organization (HMO). PATIENTS AND OTHER PARTICIPANTS: Patients with chronic health conditions (asthma, chronic obstructive pulmonary disease, or heart disease) enrolled at six intervention sites, identified through the HMO's electronic pharmacy database. Control sample with the same chronic health conditions, without access to pharmaceutical care (n = 210 participants, 162 refusers, and 368 controls; overall adjusted response rate = 72%). INTERVENTION: Pharmaceutical care, in the form of a comprehensive drug therapy management program. MAIN OUTCOME MEASURES: Predictors of participation, amount of information about medications, use of reminder methods, and awareness of side effects. RESULTS: The following variables were significantly associated with the probability of participating in pharmaceutical care (P < .05): number of medications, employment, income, health status, education, and living situation. Participants were more likely than controls to say they received "a lot of information" from their pharmacist about all aspects of medications (odds ratio [OR], 1.75 to 2.68). Participants were more likely to report leaving their medication container in a visible place and using two or more reminder methods (OR, 1.87 to 1.48). There were no significant differences in the probability of missing doses. Participants were more likely to report experiencing "symptoms or problems" associated with prescription medications (OR, 1.81). CONCLUSION: Pharmaceutical care appears to increase the information given to patients about medications, promote more effective self-administration of medications by encouraging patients to use systematic reminders, and increase awareness of medication side effects.