As public concern for quality control of medical care at the beginning of this century forced regulations on medical licensing of physicians, the forces of change in health care are again substantial, this time driven by concerns for cost and access. Our experience at the University of Pittsburgh Medical Center leads us to believe that well-trained physician extenders will play a valuable role in improving efficiency and effectiveness in the care of critically ill patients. We have developed a method for training and supervision. Graded practice supervision, with physician-led professional review, is considered a reasonable goal. We propose that the appropriate degree of supervision in any given area can be determined by: a) careful development of training programs; b) careful assessment of the individual's practice with the target patient population; and c) application of a review process that is sensitive in that population. Issues surrounding the independent practice and reimbursement of acute care nurse practitioners (ACNPs) are not resolved. These issues should be addressed by joint position statements that are based on objective documentation of the safe, effective performance of ACNPs, and on the incorporation of routine performance measurements with continued medical or joint evaluation of the quality review system. Guidelines regarding the evolving roles of ACNPs should be established by professional associations and state or national boards of both nursing and medical practice. Critical care physician and nursing leaders should lead such initiatives.