A number of experiments were carried out to explore the behavioral profile of a novel antipsychotic, risperidone, after acute or chronic administration, in a dose range of 0.1-10 mg kg-1. This drug did not affect the acquisition and retention of avoidance behaviors in a dose of 0.1 mg kg-1, either after acute or chronic administration. Higher doses induced a inhibited acquisition and a facilitated extinction (only after chronic treatment) of active avoidance behavior, but no significant effect on the retention of passive avoidance responses. In contrast, haloperidol inhibited the acquisition and facilitated the extinction of active avoidance behavior, and reduced the retention of passive avoidance reaction at the dose of 0.1 mg kg-1 injected either acutely or chronically. Ambulation and rearing of rats rated in an open field was increased by risperidone injected acutely at the dose of 1 mg kg-1. Under the same experimental conditions, grooming appeared to be reduced. In the same test, acute or chronic haloperidol 1 or 10 mg kg-1 inhibited all behavioral items. Furthermore, in contrast to haloperidol, the acute or chronic administration of risperidone in a dose range of 0.1-10 mg kg-1 did not substantially induce catalepsy and did not affect apomorphine-induced stereotypies. Also, the dose of 0.1 mg kg-1 induced a facilitation of male sexual behavior by increasing the frequency and reducing the latency of mountings, intromissions and ejaculations, while haloperidol 1 or 10 mg kg-1 inhibited this behavior. These findings suggest that the pharmacological profile of risperidone differs from that of classical neuroleptics, like haloperidol, probably due to different mechanism or site of action.