The fluid-blood barrier selectively excludes most blood-borne substances from entering the inner ear, protecting tissues from factors in the blood which would perturb the homeostasis. In her paper, Dr. Shi timely reviews current views on the structure and function, pathology and therapeutic targets of the blood barrier in the stria vascularis. The blood barrier in the stria vascularis is a specialized capillary networks in the cochlea, which also constitutes part of the blood-labyrinth barrier (BLB) in the inner ear. The primary physical diffusion barrier of the blood barrier in the stria vascularis consists of endothelial cells (ECs) connected together by tight junctions and adherens junctions. In addition to ECs, the BLB includes mural cells such as pericyte (PC) (about 1220-1330 PCs populated on capillaries in stria vascularis of a normal adult C57BL/6J mouse). PCs support the abluminal capillary wall and are embedded in the basement membrane (BM). PCs expressing platelet derived growth factor receptor-β (PDGFR-β), desmin, neural/glial antigen (NG2) and CD90, play an important role in vascular integrity, angiogenesis and BM formation. In addition to the EC and PC which are building blocks of capillaries, an interstitial cell type in the stria vascularis, named as perivascular resident macrophage typemelanocytes (PVM/Ms), situates closely to capillaries and displays the characteristics of both macrophage and melanocyte. PVM/Ms express the typical macrophage surface markers F4/80, CD68, CD11b and scavenger receptor classes A (1) and B (1), as well as the melanocyte surface markers glutathione S-transferase nalpha4 and Kir4.1. ECs, PCs and PVM/Ms together form a functional “cochlear vascular unit” in the stria vascularis. Interaction between the three cell types is critical for controlling vascular integrity, vascular permeability, providing a suitable microenvironment for hearing function.