The most challenging mission of medical personnel today is quality assurance in health care. To meet this challenge, the essential elements of a six-phase system for total quality control for the medical laboratory are outlined under the headings of design control, incoming material control, process control, output control, reliability control, and special verification studies. Review of existing goals and activities of programs related to this mission indicates both problems and rich opportunities for individual laboratory professionals and their organizations. For effective implementation of this mission, the laboratory professionals will have to create the atmosphere of a collegium where all interested scientists communicate across disciplines to eliminate the systematic biases and improve the accuracy, precision, and specificity of clinical laboratory measuring systems, to assure medically meaningful and useful assay results for the broad spectrum of health care that is necessary for the well, the near-well, and the sick.