Injections of a retrograde tracer into the accessory optic nucleus of the basal optic root (nBOR) of the pigeon, combined with 5-HT immunochemistry, revealed that serotonergic projections to the nBOR appeared to originate mainly from the median (MR) and paramedian (PMR) raphe nuclei. These projections were confirmed by the significant decrease in 5-HT immunoreactivity observed in nBOR after lesions in MR and PMR. These data characterize distinct sources of 5-HT innervation to the pigeon nBOR and suggest that those afferents could represent part of a modulatory system that contributes to the role of the nBOR in optokinetic mechanisms.