The intellectual renaissance of the closing decades of the sixteenth century provided the fertile ground in which the budding spirit of scientific inquiry emerged in the seventeenth century. Direct observation, soon augmented by instrumentation that allowed for quantification and, therefore, verification, became the revelatory medium for the progress of the sciences. In medicine, progress depended on the application of the exact sciences of chemistry, mathematics and physics to the study of function. One of the medical luminaries of this early scientific revolution was Santorio Sanctorius (1561- 1636), whose principal contributions were his studies on insensible perspiration and his instrumental inventions. To study insensible perspiration, he designed a movable platform attached to a steelyard scale that allowed for the quantification of changes in body weight of subjects who partook in their daily activities on the platform. After years of self-experimentation, he applied his device to the study of patients. Unfortunately, his records are lost. What survives is a summary of his observations in a series of aphorisms published under the title of Ars de statica medicina, in 1614; 3 years after he was appointed Ordinary Professor of Theoretical Medicine in Padua. To enhance the bedside evaluation of patients, he also designed instruments to quantify the pulse, temperature, and environmental humidity. For his pioneering and detailed balance studies, Sanctorius clearly deserves the title of founding father of metabolic balance studies.