AbstractPharmacokinetics of a novel nootropic agent, alaptide, have been examined in plasma and brain of mice, rats and rabbits following an intravenous dose (1 mg kg−1). First-order equilibration rate constants between plasma and brain (kBO) were calculated by a two-compartment model with a linked compartment (brain). Brain alaptide equilibrates rapidly with the central compartment in mice and rats due to the high kBO/β ratio. In rabbits the equilibration is much slower (kBO/β∼ 1). Partition coefficients between brain and plasma calculated from areas under the brain and plasma concentration-time curves, are 0·479, 0·549 and 0·864, in mice, rats and rabbits, respectively.