Abstract This paper analyses deliberate metaphor use in three Hippocratic treatises and in Empedocles’ two famous similes. By exclusively examining direct metaphors and their textual markers, I first investigate the communicative function metaphors have in ancient Greek anatomical and physiological argumentation. These are illustrative tools, items of evidence and/or elements that demonstrate a given hypothesis, as well as instruments of a heuristic method of enquiry. Second, I show that there are explicit claims by both authors to deliberate metaphor use: they claim to use metaphors as metaphors and leave their addressees no option but to recognise the source domain as such, as this represents the field in which both theoretical construction and the demonstration of a given hypothesis take place.