Several signalling proteins, including members of the Wnt and Hedgehog families, are lipid-modified, which can affect both their secretion and their signalling activity. Wnt proteins are modified at two sites, an N-terminal cysteine and a centrally located serine. Both residues are conserved in the Drosophila Wnt protein Wingless, which is expected to undergo the same modifications. On page 1587, Jean-Paul Vincent and colleagues use imaginal wing discs to analyse the effect of lipidation on Wingless function in vivo. Using transgenic flies that express either [C93A]Wingless (no palmitoylation site) or [S239A]Wingless (no site for the addition of palmitoleic acid), the authors show that the C93A mutant is not detectable at the cell surface, whereas the S239A mutant is present there; however, unlike wild-type Wingless, neither mutant protein spreads to nearby non-expressing cells. The authors use immunogold EM to demonstrate that the C93A mutant accumulates in the ER at a ten times higher concentration than wild-type Wingless, and is absent from multivesicular bodies (where the wild-type protein is present). Thus, the palmitoylation of Wingless is necessary for its secretion, and palmitate and palmitoleic acid are both required for its signalling activity.