The antidepressant and anxiolytic effects of alprazolam were compared to those of desipramine, diazepam and buspirone in the forced swim test. Subchronic alprazolam induced a reduction in immobility similar to that of desipramine in 'non-pretested' and 'pretested' rats. In 'non-pretested' rats, the anti-immobility effect of desipramine was potentiated by diazepam and alprazolam, given before subchronic desipramine, while the anti-immobility effect of subchronic alprazolam was counteracted by diazepam. Diazepam, administered before the pretest session, counteracted, 24 h later, the anti-immobility effect of subchronic desipramine and alprazolam; alprazolam counteracted the anti-immobility effect of alprazolam but not of desipramine, buspirone at the highest doses tested potentiated the anti-immobility effect of subchronic desipramine but not of alprazolam. These data provide further support for the hypothesis that the GABA/benzodiazepine/Cl complex is directly implicated in the action of antidepressants and that systems other than the GABA system are involved in the antidepressant and anxiolytic effects of alprazolam.