Primary care research consists of four types: basic, clinical, health services, and health systems. Basic research addresses the development of methods to study subjects relevant to primary care services, regardless of whether they deal with a clinical problem or a characteristic of service delivery. Clinical research involves issues relevant to the processes of delivering services, including recognition of people's problems, diagnostic approaches, and types of therapy and their outcomes. Health services research concerns the relationships associated with the organization and financing and their impact on the processes and outcomes of care. Health systems research focuses on understanding how the economic, political, and social milieus influence the structures and processes of the health services system, with specific relevance to its primary care infrastructure. The literature on primary care, as reflected by publications in three major general journals, is notably lacking in specific areas of study within these types of primary care research, particularly with regard to basic and health services research.