To describe the evidence that preventable adverse outcomes of drug therapy are prevalent in the United States and Europe, to describe the causes of this problem, to outline a systems response that would correct or improve the problem, to discuss pharmacy's contribution to that solution, and to propose a strategy for implementation. The causes of the widespread problem of preventable drug-related morbidity (PDRM) that have been identified in the literature constitute system failure. Health professionals can understand an individual patient's care system if they organize their thinking about systems as efficiently as they organize their thinking about medical or pharmaceutical problems. Six essential system characteristics are proposed, based on the PDRM literature. Regulations should mandate regular patient and system performance assessments--specifically, that health professionals (1) identify, resolve, and document specific pharmacotherapy problems; (2) assess system performance and identify recurring root causes of problems; and (3) document assessments, problems found, actions taken, and follow-up. These regulations would, in essence, mandate individual quality improvement (QI) programs. QI and pharmaceutical care require similar processes of decisions and actions, one from a practice (multipatient) perspective and the other from a patient perspective. Health care accreditation agencies are moving toward regulation for outcomes. Pharmacy managers should embrace and regulatory boards should participate in this movement. Such regulations would clarify pharmacy's role in support of safe and effective pharmacotherapy and would constitute a commitment to pharmaceutical care as public service. A widely adopted system of measuring and improving the quality of medication use and outcomes could eventually lead to quality benchmarks in the community pharmacy setting, which would more firmly establish the value of the pharmacist in pharmacotherapy.