Numerous studies have shown that ingrowing olfactory axons exert powerful inductive influences on olfactory map development. From an overexpression screen, we have identified wnt5 as a potent organizer of the olfactory map in Drosophila melanogaster. Loss of wnt5 resulted in severe derangement of the glomerular pattern, whereas overexpression of wnt5 resulted in the formation of ectopic midline glomeruli. Cell type-specific cDNA rescue and mosaic experiments showed that wnt5 functions in olfactory neurons. Mutation of the derailed (drl) gene, encoding a receptor for Wnt5, resulted in derangement of the glomerular map, ectopic midline glomeruli and the accumulation of Wnt5 at the midline. We show here that drl functions in glial cells, where it acts upstream of wnt5 to modulate its function in glomerular patterning. Our findings establish wnt5 as an anterograde signal that is expressed by olfactory axons and demonstrate a previously unappreciated, yet powerful, role for glia in patterning the Drosophila olfactory map.