The action of a selective 5-HT1A agonist S20244 and its two enantiomers (+)-S20499 and (-)-S20500 were assessed in mice. The animals were confronted with a free exploratory test especially adapted to reveal behavioural sedation, and with a two-box light/dark choice situation validated for the detection of anti-anxiety agents. These drugs were found to have anxiolytic properties at low doses, like benzodiazepines. Furthermore, the drugs exhibited sedative effects at higher doses. These results closely resemble those we found after administration of two other 5-HT1A agonists, 8-OH-DPAT and MDL 73005EF (NeuroReport, 1, 267-270, 1990).