Drosophila flies with the trp mutation exhibit impaired vision due to the lack of a specific Ca2+ influx pathway in the photoreceptors. The identification of the trp gene product as a Ca2+-permeable ion channel and the search for TRP homologues in flies, worms and mammals has opened the way to the discovery of a whole superfamily of cation channels, baptized TRP channels. In contrast to voltage-gated K+, Na+, or Ca2+ channels, with whom they share their transmembrane architecture, TRP channels are not activated by voltage but by a variety of signals including intra- and extracellular ligands, Ca2+-store depletion and mechanical or thermal stress. Due to the promiscuity of these gating mechanisms, TRP channels are privileged candidates as primary sensing molecules for the recognition and integration of physical and chemical signals from the environment. In this review we discuss recent evidence that implicates members of the TRP superfamily in sensory signal transduction.