The structure and interrelations of the biomedical journal literature are investigated as a preparatory step for studies of biomedical research activity. Using newly developed methods of bibliographic citation analysis, approximately 900 biomedical journals are classified into approximately 50 separate fields and into four research levels. The research-level scale indicates research orientation ranging from clinical observation to basic research. Measures of influence are then obtained for individual journals, for biomedical fields and for research levels. The fields of biochemistry and physiology are shown to have the highest citation influence.

A hierarchical influence diagram is presented to display the influence of 42 fields within biomedicine. Hierarchical influence diagrams are also presented for several individual fields showing the influence structure and citation relationships among their component journals. The combination of a subject, a level and an influence measure provides a unified framework for planned research activity analysis.