This review examines the use of transporter knockout (KO) animals to evaluate transporter function at the choroid plexus (the blood-CSF barrier; BCSFB). Compared to the blood-brain barrier, there have been few such studies on choroid plexus (CP) function. These have primarily focused on Pept2 (an oligopeptide transporter), ATP-binding cassette (ABC) transporters, Oat3 (an organic anion transporter), Svct2 (an ascorbic acid transporter), transthyretin, ion transporters, and ion and water channels. This review focuses on the knowledge gained from such studies, both with respect to specific transporters and in general to the role of the CP and its impact on brain parenchyma. It also discusses the pros and cons of using KO animals in such studies and the technical approaches that can be used.