The substituted benzamide amisulpride is currently administered in its racemic form. In the present study, the biochemical and cataleptogenic profiles of the two enantiomers (R+ and S-) were compared with those of the racemic mixture. Displacement binding studies showed that the (S-)-isomer possesses an higher affinity for dopamine D2-like receptor (K(i) 5.2+/-0.4 nM) compared to (R+)-amisulpride (K(i) 244+/-12 nM) and to (RS)-amisulpride (K(i) 9.8+/-0.8 nM). In contrast, (S-)-amisulpride binds the alpha(2)-receptor with an affinity (K(i) 1528+/-45 nM) lower than that of the (R+)-isomer (K(i) 375+/-34 nM) and of (RS)-amisulpride (K(i) 783+/-27 nM). The bar test was used to evaluate the catalepsy induced by each drug. (RS)-amisulpride induced catalepsy only at very high doses (>100 mg/kg, s.c.) whereas, (S-)-amisulpride produced a catalepsy at a lower dose (30 mg/kg, s.c.) and (R+)-amisulpride did not produce any catalepsy up to the dose of 75 mg/kg. Interestingly, (R+)-amisulpride reduced the catalepsy induced by (S-)-amisulpride (50 mg/kg, s.c.) or haloperidol (0.3 mg/kg, s.c.), at the doses of 50 or 30 mg/kg, respectively. These results indicate that the weak cataleptic properties of (RS)-amisulpride might partially rely on its (R+)-isomer and provide a further explanation for the atypical properties of amisulpride as an antipsychotic.