D-Serine, a selective agonist at the strychnine-insensitive glycine binding site, antagonized PCP-induction of stereotyped behavior and ataxia in a dose-dependent manner. At intraventricular doses of 0.1, 0.5 and 1 mumol/rat, D-serine significantly attenuated PCP-induction of stereotyped behavior in rats. Only doses of 0.5 and 1.0 mumol/rat of D-serine antagonized PCP-induction of ataxia. D-Serine (0.5 mumol/rat) also antagonized MK-801 induced stereotyped behavior and ataxia. These results suggest that agonists at the strychnine-insensitive glycine site may be clinically useful as a novel class of atypical antipsychotic agents.