As part of our investigations of compounds with potential affinity to the glycine binding site of the NMDA receptor, the structure of ethyl-N-[(p-Cl-benzylidene)-4-oxo-2-imidazolidyl]glycinate hydrochloride is reported: C 1 4 H 1 4 N 3 O 3 Cl.x HCl; monoclinic; Pc; a=5.015(1), b=16.891(3), c=10.160(2) 9, β=101.76(3) o ; V=842.6(3) 9 3 ; Z= 2; D x =1.357gcm - 3 ; λ(Cu Kα)=1.54178 9; μ=36.0mm - 1 ; final R=0.0482 for 803 reflections [I>4σ(I)]. The molecule was found to have a Z-configuration and three Cl...H-N bonds were identified. These are believed to be crucial in interpreting the ligand-receptor interaction mode in the glycine-binding site. Searches of the IsoStar database were also used to help to justify the proposed model.