Increasing amounts of medical knowledge, clinical data, and patient expectations have created a fertile environment for developing and using clinical practice guidelines. Electronic medical records have provided an opportunity to invoke guidelines during the everyday practice of clinical medicine to improve health care quality and control costs. In this paper, efforts to incorporate complex guidelines [those for heart failure from the Agency for Health Care Policy and Research (AHCPR)] into a network of physicians' interactive microcomputer workstations are reported. The task proved difficult because the guidelines often lack explicit definitions (e.g., for symptom severity and adverse events) that are necessary to navigate the AHCPR algorithm. They also focus more on errors of omission (not doing the right thing) than on errors of commission (doing the wrong thing) and do not account for comorbid conditions, concurrent drug therapy, or the timing of most interventions and follow-up. As they stand, the heart failure guidelines give good general guidance to individual practitioners, but cannot be used to assess quality or care without extensive "translation" into the local environment. Specific recommendations are made so that future guidelines will prove useful to a wide range of prospective users.