The development of laboratory testing to diagnose and treat human disease has progressed steadily from mere observation of bodily fluids in ancient times to the 17th century invention of the microscope and the discovery of microscopic organisms and structures. Today the specialty of clinical pathology, or laboratory medicine, plays an increasingly major role in clinical care. Physicians rely on the timely and accurate testing of their patients’ fluids to assist them in diagnosing an ever-expanding range of pathologies. The development of university programs in medical technology and residency programs in clinical pathology have supported this development. The University of Washington is a leader in the field. From the Series:Laboratory Medicine Grand Rounds