Objectives-To examine the influence of evidence-based guidance on health care decisions, a study of the use of seven different sources and types of evidence-based guidance was carried out in senior health professionals in England with responsibilities either for directing and purchasing health care based in the health authorities, or providing clinical care to patients in trust hospitals or in primary care. Design-Postal survey. Setting-Three health settings: 46 health authorities, 162 acute and/or community trust hospitals, and 96 primary care groups in England. Sample-566 subjects (46 directors of public health, 49 directors of purchasing, 375 clinical directors/consultants in hospitals, and 96 lead general practitioners). Main outcome measures-Knowledge of selected evidence-based guidance, previous use ever, beliefs in quality, usefulness, and perceived influence on practice. Results-A usable response rate of 73% (407/560) was achieved; 82% (334/407) of respondents had consulted at least one source of evidence-based guidance ever in the past. Professionals in the health authorities were much more likely to be aware of the evidence-based guidance and had consulted more sources (mean number of different guidelines consulted 4.3) than either the hospital consultants (mean 1.9) or GPs in primary care (mean 1.8). There was little variation in the belief that the evidence-based guidance was of "good quality", but respondents from the health authorities (87%) were significantly more likely than either hospital consultants (52%) or GPs (57%) to perceive that any of the specified evidence-based guidance had influenced a change of practice. Across all settings, the least used route to accessing evidence-based guidance was the Internet. For several sources an effect was observed between use ever, the health region where the health professional worked, and the region where the guidance was produced or published. This was evident for some national sources as well as in those initiatives produced locally with predominantly local distribution networks. Conclusions-The evidence-based guidance specified was significantly more likely to be seen to have contributed to the decisions of public health specialists and commissioners than those of consultants in hospitals or of GPs in a primary care setting. Appropriate information support and dissemination systems that increase awareness, access, and use of evidence-based guidance at the clinical interface should be developed.