5-Hydroxytryptamine exerts modulatory physiological effects on both the central and peripheral nervous systems by activation of discrete receptor families. 5-ht(5A) is among the recently cloned, novel 5-HT receptors and currently under investigation to identify its pharmacological characteristics and potential physiological function(s). In this study, antibodies raised to a 5-ht(5A)-specific peptide were characterized using dot blot, sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunohistochemistry, and the distribution of 5-ht(5A)-like immunoreactive material determined in rat brain. A major band of 41 kDa was observed following SDS-PAGE, corresponding to the predicted size of this receptor. 5-ht(5A)-like immunoreactivity was detected in areas known to have significant serotonergic input, such as hypothalamic and amygdaloid nuclei. Interestingly, 5-ht(5A)-like immunoreactivity showed a predilection for the suprachiasmatic nucleus, suggesting its possible role in the regulation of circadian rhythms, a function previously ascribed to 5-HT(1A) and 5-HT(7) receptors.