Metapramine, a pharmacological compound with antidepressant activity in humans, was tested for possible antiglutamatergic activity, in vitro. We investigated the effects of metapramine on the N-methyl-D-aspartic acid (NMDA) receptor complex, by determining whether this compound would interfere with the binding of [3H]N-[1-(2-thienyl)cyclohexyl]-3,4-piperidine ([3H]TCP) to rat cortical membranes in the presence of either glycine NMDA, or both. Metapramine in the micromolar range inhibited the binding of [3H]TCP in the presence of both NMDA and glycine (IC50 = 1.4 +/- 0.2 microM). That very similar affinities were observed when either NMDA or glycine was present suggests that metapramine exerted a direct action at the PCP site. The affinity of metapramine for this site was about 25 and 350 times lower than that of PCP and MK-801, respectively. Metapramine inhibited the NMDA-evoked increase in guanosine 3',5'-cyclic monophosphate (cGMP) levels of neonatal rat cerebellar slices (IC50 = 13 microM). These results suggest that metapramine is a low-affinity antagonist of the NMDA receptor complex channel. This paper discusses the potential application of metapramine to the treatment of diseases linked to excessive stimulation of glutamatergic NMDA receptors.