the main purpose of this paper is to examine the reaction of aristotle and the stoic chrysippus to a metaphysical problem that has been overlooked in recent studies of ancient physics. the problem concerns the generation of the so-called homogeneous complex bodies. if, as these authors maintain, such bodies are generated by a mixture of more basic bodies, and if they are destroyed when this mixture is dissolved and the original ingredients separate themselves from each other, then, a dilema seems to arise: during the existence of the complex body (i) either the simple bodies persist as such within the complex body, in which case it appears that this latter could not be homogeneous, (ii) or the simple bodies are destroyed when the complex body is generated, in which case an explanation is needed of how the former obtain again when the latter is dissolved. at the end, i also offer an analysis of how chrysippus gives support to the thesis itself that complex homogeneous bodies are the result of a mixture of simpler bodies. the whole is preceded by an account of how his theory of mixture fits with his general theory of the generation of natural bodies.