Glycine as a cofactor of NMDA receptor has an indispensable role for NMDA receptors in its function. Glycine level is controlled by glycine transporter type 1 (GlyT-1) in the synaptic cleft. GlyT-1 takes place on the membrane of glial cells and controlling the glycine concentration is involved in many CNS functions, as well. Hypofunction of the NMDA glutamate transmitter system is emerging as a potentially promising hypothesis in the pathology of schizophrenia. The increase in glycine concentration can ameliorate the hypofunction of this system. Glycine concentration elevation in the brain can be achieved experimentally or in the clinics by administration of glycine or by GlyT-1 inhibitors. Methyl-glycine, NFPS, Org24461 and SSR504735 are the investigated inhibitors in detail. The GlyT-1 is measured mainly by functional tests, essentially by measuring the amount of tritiated glycine taken up the cells. The uptake is linear with time until the concentration ratio between outside and inside the cells approaches equilibrium. The concentration ratios of glycine and Na+/Cl- ions are the driving force of the glycine transport. While the transportable and competitive inhibitors start to inhibit GlyT-1 immediately after their addition, the effect of the non-transportable, non-competitive inhibitors develops slowly, as the compounds bind to the receptor and the binding results in conformation changes, stopping the glycine transport fully or partially. Our aims are the systematic investigation of some GlyT-1 the inhibitors’ kinetics using functional tests. We determined the association and dissociation velocities. The virtual IC50 values depend on the experimental conditions. The slow association and dissociation may have clinical implications.