The distribution and the morphology of nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase (ND)-active and neuronal nitric oxide synthase (NOS)-immunoreactive neurons and fibers were studied in the olfactory bulb of three species of primates, i.e., the cynomolgus macaque monkey (Macaca fascicularis), the Japanese macaque monkey (Macaca fuscata), and the pig-tail macaque monkey (Macaca nemestrina). The ND staining was carried out by means of a direct histochemical method with beta-NADPH as cosubstrate and nitro blue tetrazolium as chromogen. The NOS immunostaining was carried out by using a polyclonal antibody and the avidin-biotin peroxidase method. Similar results were found in the three species, where a distinct distribution pattern of ND/NOS-stained neurons and fibers was observed. All olfactory fibers demonstrated ND-positive labeling but they were NOS-immunonegative. In the superficial modulatory area of the olfactory bulb, a few weakly ND- and NOS-positive periglomerular cells, stellate cells, and darkly stained superficial short-axon cells were observed. In the inframitral layers, granule cells, deep stellate cells, and deep short-axon cells were distinguished. Short-axon cells had oriented morphologies and spiny dendrites. Many thick, varicose ND/NOS-stained fibers identified as centrifugal fibers were observed in the white matter, granule cell layer, internal plexiform layer, mitral cell layer, and external plexiform layer. This distribution of ND activity and NOS immunoreactivity showed similarities to and differences from what has been reported in the olfactory bulb of macrosmatic mammals including rodents (rat, mouse, and hamster) and insectivores (hedgehog). These data confirm that the complexity of the ND/NOS staining in the olfactory bulb of one species correlates with the importance of olfaction in the biology of such species.