Teaching physiology implies the transmission of facts and scientific methodology. These have widely different epistemological status. Facts keep increasing in quantity, can be retrieved easily and their relevance changes with time. Methodology has not changed since Galileo and can be apprehended at best working in close association with the "Master". Teaching of medical matters has been traditionally subdivided in pre-clinical and clinical areas, the first of which was devoted to facts and laws of the basic sciences and to the relevant methodology, the aim of which is to infer the laws governing a living system, as follows. The system is artfully perturbed (independent variable); a response governed by its intrinsic laws (unknown) follows; the resulting response (dependent variable) is observed. The following years were devoted to the clinical sciences and to the relevant methodology, the aim of which is to identify and eliminate the causes of illness, as follows. The patient responds to an (unknown) perturbation on the bases of the laws apprehended in the previous years (independent variable); the response of the patient is observed (dependent variable). The so-called PBL (problem based learning), wherein the student is thrown "in medias res" without a clear separation between facts and methodology, has recently gained wide acceptance in the medical schools. Advantages and disadvantages of the traditional and PBL approaches for teaching human physiology will be discussed.