The writings of Galen are an important source of information about Erasistratus. A comprehensive analysis of this source material provides an idea of Erasistratus’s and his followers’ approaches to solving practical problems of clinical medicine. The article’s author cites arguments confirming that Erasistratus’s clinical practice, the basis of which was the natural philosophy of atomism, should be considered as the foundation of methodologists’ teachings. Methodist physicians, guided by Erasistratus’s medical postulates, needed a theory that logically explained the phenomena they observed, while for rationalist physicians theoretical medicine was the impetus for experimental studies, the results of which became its foundation.