Intravenous adeno-associated viral vector serotype 9 (AAV9) transduces neurons, astrocytes, and vessels but not microglia in the brain. Following intrajugular vein administration of viral vectors at the titers/doses used in this study, double-label immunofluorescence demonstrates colocalization of (a,d,g,j) enhanced green fluorescent protein (eGFP)–positive cells: (b,c) NeuN-labeled neurons, (e,f) glial fibrillary acidic protein (GFAP)–labeled astrocytes, (k,l) CD31-labeled vascular endothelial cells but not (h,i) Iba1-labeled microglia in the mouse brain. Bar = 25 µm.