Mapping long-range neuronal projections with high resolution and high throughput has proved difficult. In an attempt to achieve this goal, Kebschull et al. developed a method termed multiplex analysis of projections by sequencing (MAP-seq). In mice, they injected the locus coeruleus (LC) with a viral library encoding a large pool of diverse mRNA 'barcodes', so that most infected neurons expressed only one such barcode. As the virus expressed a protein that promoted barcode transport to axon terminals, the authors could extract mRNA from the LC and distal sites and, through barcode sequencing, quickly determine the projection sites of many individual LC neurons.