Two new studies reveal crucial roles for MFSD2A (major facilitator superfamily domain-containing protein 2A) in blood–brain barrier (BBB) development and function. Nguyen et al. showed in mice that MFSD2A was expressed in the endothelium that comprises the BBB at embryonic day 15.5 (E15.5) and in adulthood. Mfsd2a−/− mice exhibited various motor and cognitive deficits and decreases in neuronal number in certain brain regions. These mice also had low brain levels of docosahexaenoic acid (DHC), an omega 3 fatty acid, and cell-based assays revealed that MFSD2A can transport DHC when it is attached to the lipid lysophosphatidylcholine. In the other study, Ben-Zvi et al. established that the mouse BBB becomes functional at E15.5 and that this milestone is preceded by an increase in Mfsd2a expression in the CNS vasculature. They also found that embryonic and postnatal Mfsd2a−/− mice had a leaky BBB that was caused by increased CNS endothelial cell vesicular transcytosis. Thus, MFSD2A regulates both DHC transport into the brain and vesicle transport across the BBB.