In this paper, I discuss the aetiological account of biological interests, developed by Varner (1998), in the context of artefactual organisms envisioned by current research in synthetic biology. In "Sections 2–5", I present Varner's theory and criticise it for being incapable of ascribing non-derivative interests to artefactual organisms due to their lack of a history of natural selection. In "Sections 6–7", I develop a new alternative to Varner's account, building on the organisational theory of biological teleology and function. I argue that the organisational account of biological interest is superior to Varner's aetiological account because it (i) can accommodate both artefactual and naturally evolved organisms, (ii) provides a non-arbitrary and practical way of determining biological interests, (iii) supports the claim that organisms have interests in a sense in which artefacts do not, and (iv) avoids the possibility of there being a conflict between what an organismic part is supposed to do and what is in the interest of the organism.