The study investigates hippocampal neurogenesis in adult Old World monkeys, a group previously thought to lack this process. Researchers injected 11 adult macaque monkeys with bromodeoxyuridine (BrdUrd), a thymidine analog that labels dividing cells, and examined the fate of these cells using neuronal and glial markers. In young-adult and middle-aged monkeys, a substantial number of BrdUrd-labeled cells exhibited characteristics of both immature and mature granule neurons. These cells expressed markers such as Turned On After Division 64 kDa protein (TOAD-64), neuron-specific enolase (NSE), neuronal nuclei (NeuN), and calbindin. Fewer labeled cells expressed glial fibrillary acidic protein (GFAP). Evidence of neurogenesis was also observed in older monkeys (23 years), though it was less robust. These findings suggest that adult Old World monkeys produce new hippocampal neurons, providing a primate model for studying the functional significance of adult neurogenesis. The study challenges previous reports of no neurogenesis in adult macaque monkeys using 3H-thymidine autoradiography, possibly due to longer survival times post-injection. The results highlight the potential for promoting the survival of new neurons through environmental enrichment and suggest that hippocampal neurogenesis may play a crucial role in learning and memory.The study investigates hippocampal neurogenesis in adult Old World monkeys, a group previously thought to lack this process. Researchers injected 11 adult macaque monkeys with bromodeoxyuridine (BrdUrd), a thymidine analog that labels dividing cells, and examined the fate of these cells using neuronal and glial markers. In young-adult and middle-aged monkeys, a substantial number of BrdUrd-labeled cells exhibited characteristics of both immature and mature granule neurons. These cells expressed markers such as Turned On After Division 64 kDa protein (TOAD-64), neuron-specific enolase (NSE), neuronal nuclei (NeuN), and calbindin. Fewer labeled cells expressed glial fibrillary acidic protein (GFAP). Evidence of neurogenesis was also observed in older monkeys (23 years), though it was less robust. These findings suggest that adult Old World monkeys produce new hippocampal neurons, providing a primate model for studying the functional significance of adult neurogenesis. The study challenges previous reports of no neurogenesis in adult macaque monkeys using 3H-thymidine autoradiography, possibly due to longer survival times post-injection. The results highlight the potential for promoting the survival of new neurons through environmental enrichment and suggest that hippocampal neurogenesis may play a crucial role in learning and memory.