As traditional medical school curricula began to be criticized in the 1950s, various alternatives were proposed, including the organ-system based curriculum (organized around the organ systems of the body) and the problem-based curriculum (organized around clinical problems). From an open systems perspective, any such medical school curriculum change raises questions about the innovations's potential effect on all three sectors of the institution: education, service (patient care), and research. Analysis of the planning process involved in curriculum change thus includes three dimensions: centrality (priority within a school's total set of objectives), locus (location of the institutional decision-making apparatus), and inclusivity (implications for other noncurricular activities). Two case studies of the efforts of one well-established and one recently established medical school to institute organ-system-based and problem-based curriculum change reveal quite different experiences. Results of the studies--based on interviews, analysis of written materials, and observation--confirm three general hypotheses: the more central an innovation to the institution's goals, the more likely it is to be maintained; the institutional locus of planning that maintains the innovation will parallel the locus of power; the more inclusive the innovation, the more likely it is to be maintained. (JBM)