Galen’s physiology has notably provided explanation of the causes of diseases in terms of alteration to the balance of qualities (eukrasia), and the consequent dominance of one quality over the others. If this is quite evident and extensively illustrated by Galen himself on a number of occasions in reference to diseases affecting the body, the organs, and their composition (kataskeuè), when the diseases affect the soul it is more difficult to find a precise physiological explanation that details any such unbalance. In spite of this, in qam Galen refers to the influence that alterations of the body have on the affections of the soul and, in addition, in his ethical works he insists on the role of the physician and his responsibility in reference to the behaviours of his patients. Galen certainly has in mind the model of integrity that the physician has to provide, but is there more to it than that? If the alteration of the bodily mixtures has consequences for the behaviour of the patients, would the knowledge and the ability to master the kraseis owned by the physician imply an ethical responsibility linked to this profession? The aim of this paper is to detect and illustrate the links between the theory of mixtures and the implications it may have in the domain of ethics, taking into consideration both Galen’s physiological and ethical works.