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Abstract: Glycine can act as either an inhibitory neurotransmitter or as a potentiator of NMDA-dependent excitatory neurotransmission. There is some evidence that glycine can have both pro- and anticonvulsant properties in various rodent models of epilepsy. In the present study we tested several glycine transporter 1 (GlyT1) inhibitors including NFPS, SSR 504734, Lu AA21279, Org 25935, SB-710622, GSK931145, as well as the glycine agonist d-serine, in the maximal electroshock threshold (MEST) test in the rat. In a series of experiments, male Sprague–Dawley rats (n =12/group) were pre-treated with a compound of interest and then received an electric shock delivered via corneal electrodes. A cohort of satellite animals (n =3/group) was also used to measure blood and brain levels of Org 25935. All GlyT1 inhibitors increased seizure thresholds dose-dependently, indicative of anticonvulsant activity. SB-710622 and GSK931145 had lower minimum effective doses (MEDs) in the MEST test than other GlyT1 inhibitors. At estimated t max, increases in dose administered were paralleled by increases in blood and brain concentrations of Org 25935. Thus, increasing extracellular concentration of glycine via inhibition of its uptake protects from electroshock-induced seizures in the rat. Whether strychnine-sensitive or strychnine-insensitive glycine binding sites are involved in this effect remains to be determined. [Copyright &y& Elsevier]