The involvement of serotonergic receptor subtypes in modulation of rat behavior in a black and white test box was studied. The high efficacy 5-HT(1A) receptor agonist 8-OH-DPAT [8-hydroxy-2-(di-n-propylamino)tetraline] was inactive, and the partial agonist buspirone showed an anxiolytic-like response that was weaker than the response to diazepam. The non-selective 5-HT(1) receptor agonists TFMPP [1-(trifluoromethylphenyl) piperazine] and eltoprazine were inactive. Low doses of the 5-HT(1A) receptor antagonist WAY 100.635 [N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclohexanecarboxamide] induced an anxiolytic-like response; 10-100 times higher doses induced an anxiogenic-like response. The 5-HT(2A/2C) and 5-HT(3) receptor antagonists ritanserin and ondansetron induced anxiolytic-like responses. The 5-HT(2A/2C) receptor agonist DOI [1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane] and the 5-HT(2A) receptor antagonist-MDL 100.151 [(=) chi-(2,3-dimethoxyphenyl)-1-[2-(4-fluorphenyl)ethyl]-4-piperidin-methanol] were inactive. 8-OH-DPAT potentiated the anxiolytic-like effect of ritanserin. It is suggested that 5-HT(1A) and 5-HT(2C) receptors are involved in mediation of exploratory behavior in rats, and that the 5-HT receptor subtype mediated effects may modulate one another.