BACKGROUND: Studies of clinical guideline implementation have focused almost entirely on changing individual clinician behavior with single intervention strategies and without much attention to the situational context. The goal of this project was to learn from clinic leaders, seasoned in the guideline implementation process, what contextual variables they viewed as important and whether implementation success could be expected if only a single implementation strategy was used. METHODS: In 1998, 12 people with extensive experience in leading clinical guideline implementation were identified who were thought to have particularly keen insight into the process. They were interviewed to generate variables they considered important, as well as strategies they considered effective when used appropriately. A modified nominal group/Delphi process was then used for rating these variables and strategies, and the reactions of international experts were obtained to add perspective to this information. RESULTS: Eighty-seven variables and 25 strategies were identified, clustering in 6 categories (ranked in order of importance by the panel): organizational capabilities for change, infrastructure for implementation, implementation strategies, medical group characteristics, guideline characteristics, and external environment. All six categories were considered to be important, key, or essential by the experienced implementers, although variables within a medical group that directly affect its ability to undertake planned change were rated as much more important than either guideline characteristics or the external environment. DISCUSSION: Although the opinions of those experienced in the process of guideline implementation are primarily of value for generating hypotheses, panel members believe that implementation efforts focusing on the individual physician with a single strategy are unlikely to be successful. Rather, implementation efforts must use multiple strategies that take account of multiple characteristics of the guideline, practice organization, and external environment.