Development of the Drosophila tracheal system – the fly respiratory network – is known to require the chitin deacetylase serpentine (Serp), which is expressed in tracheal epithelial cells. Here, Shigeo Hayashi and co-workers show that Serp derived from the Drosophila fat body, which is functionally equivalent to the mammalian liver, is transported to the tracheal lumen and is required for tube morphogenesis (p. 4104). They first show that Serp is expressed in the fat body and that Serp levels accumulate in fat bodies of the rab9 and shrub vesicle trafficking mutants. By contrast, Serp levels in the tracheal lumen of these mutants are reduced, suggesting that Serp is secreted into the haemolymph and is taken up by tracheal cells. Importantly, the researchers show that fat body-derived Serp is able to rescue the tracheal defects observed in serp mutants. These studies suggest that Serp should be added to the expanding repertoire of proteins that the fat body supplies to other organs and highlight the role of the fat body in regulating the development of other organs.