Choroid plexi from the lateral ventricles of rabbits, cats, and dogfish (Mustelus canis) were used to characterize the prostaglandin (PG) uptake process and to establish its kinetic parameters and substrate specificity. The apparent K_t for PGF_2α transport by the rabbit choroid plexus was 20 μM; the J_max was 27 nmol g⁻¹ mm⁻¹. The K_i of inhibition of PGF_2α transport by PGE₂ was 20 μM; the J_max of PGF_2α transport was unaltered by PGE₂. A concentration of p‐aminohippuric acid of up to 1 mM did not appreciably affect the K₁ or the J_max of PGF_2α transport. The rate of PGF_2α accumulation by rabbit choroid plexus was reduced by incubation at 4°C, under anaerobic conditions, in the absence of sodium or in the presence of ouabain, probenecid, or bromcresol green. The choroid plexi of all three species also accumulated thromboxane B₂, PGI₂, and 6‐keto‐PGF_1α, suggesting that most, if not all, eicosanoids are substrates for this transport system. It is concluded that the choroid plexus transport system satisfies all the criteria of an active, energy‐dependent transport system and that this system functions effectively at concentrations of eicosanoids present in the ventricular system under normal or pathological conditions. Hence, this transport system must make an important contribution to the pharmacokinetics of eicosanoids within the brain.