The purpose of the present paper was to determine whether the brief exposure of neurons to antipsychotic drugs is associated with the activation of extracellular signal-regulated kinases (ERK) and cyclic adenosine 3',5'-monophosphate (cAMP) response element (CRE) binding protein (CREB). The activation of ERK-1/2 and CREB can be monitored by immunoblotting with antibodies that specifically recognize p-ERK-1/2 (phosphorylated on Thr-202 and Tyr-204) and p-CREB (phosphorylated on Ser-133). In hippocampal neuron cultures at 25 days in vitro (DIV), the levels of ERK and CREB phosphorylation significantly increased after treatment with haloperidol (50 nmol/L) and risperidone (50 nmol/L), except when risperidone was administered at the p-CREB level. However, risperidone also increased the p-CREB level at an insignificant rate in the same direction. At 10 DIV, none of the antipsychotic drugs significantly increased the level of ERK and CREB phosphorylation. The difference between levels of ERK and CREB phosphorylation in response to haloperidol and risperidone at 25 DIV was also observed. Risperidone significantly increased the level of ERK-1/2 phosphorylation, but not the level of CREB phosphorylation. Haloperidol, in contrast, had a different effect. These data indicate that neuronal maturation affects the phosphorylation of ERK and CREB in response to antipsychotic drugs. Furthermore, these results demonstrate that different antipsychotic drugs could lead to different profiles of ERK and CREB phosphorylation in neurons.