1. Lignocaine readily passes from blood into cerebrospinal fluid. The isolated rabbit choroid plexus, a locus of the blood—cerebrospinal fluid barrier, accumulated [14C]lignocaine by two processes: an active, saturable transport process and a non-saturable process. 2. The accumulation of [14C]lignocaine by choroid plexus was not due to non-specific binding or metabolism of lignocaine within or on the choroid plexus. 3. These results suggest that the choroid plexus may transport lignocaine between blood and cerebrospinal fluid in vivo by a specific carrier-mediated process.