In the olfactory system of Drosophila, sensory neurons synapse with projection neurons in specifically positioned structures called glomeruli. The relatively conserved pattern of olfactory glomeruli between individuals suggests that their formation is organised by a robust developmental program. Jhaveri and colleagues examined the role played by Roundabout (Robo) – the receptor for the diffusible ligand Slit –during the positioning of glomeruli(p. 1903). They found that different populations of olfactory sensory neurons express different combinations of Robo, Robo2 and Robo3 at different times during development. Furthermore, disrupting the expression of these proteins in specific neurons results in changes in glomerular organisation. They also showed that by manipulating Slit levels, they could alter the terminal positioning of sensory neurons. The researchers suggest that the combinational code of Robo receptors and their response to Slit levels guides sensory neurons to unique positions in the olfactory lobe.