Activation of the archetypal Transient Receptor Potential (TRP) channel, which is essential for Drosophila phototransduction, depends on a phospholipase C (PLC). However, the precise mechanism linking PLC to the gating of TRP has been elusive. In this issue of Neuron, Leung et al. provide compelling evidence that a diacylglycerol (DAG) lipase (INAE), acting downstream of the PLC, is essential for opening TRP. These results strongly support the model that a DAG metabolite is critical for TRP activation and suggest that mammalian DAG lipases may play similar roles.