Dumuis and colleagues (1988) in their investigation of a 5-HT receptor positively linked to adenylate cyclase in the central nervous system, concluded that the receptor was not 5-HT1, 5-HT2 or 5-HT3-like and suggested that it belonged to a new class of 5-HT receptor called 5-HT4. A similar, if not identical receptor was located by Craig and Clark (1990) in the guinea pig ileum and a functional role for the peripheral 5-HT4 receptor has since been established in many species to mediate muscle contraction or relaxation within the gut and positive inotropic effects in the heart. In contrast, a functional role for central 5-HT4 receptors has remained obscure. Using measurements of rodent behaviour in the mouse light and dark test box and rat social interaction, anxiolytic agents such as diazepam and putative anxiolytic agents such as the 5-HT1A and 5-HT3 receptor ligands 8-OH-DPAT and low doses of tropisetron release behaviour suppressed by the aversive situation. 5-Hydroxytryptophan has the opposite effect exacerbating the behavioural response to the aversive situation. But an anxiolytic profile is revealed by co-treatment with ritanserin plus 5-hydroxytryptophan. The drug-induced anxiolytic profiles are inhibited by SDZ205-557 and a high dose of tropisetron. Both compounds are 5-HT3/5-HT4 receptor antagonists yet the selective 5-HT3 receptor antagonist ondansetron fails to inhibit the drug-induced anxiolytic profiles.(ABSTRACT TRUNCATED AT 250 WORDS)