Diapause hormone (DH) originally identified to be a factor originating from neurosecretory cells in the suboesophageal ganglion acts on developing ovaries to produce diapause eggs in a female silkmoth, Bombyx mori. A male silkmoth has homologous neurosecretory cells, but little is known of the physiological nature of the cells and actions of their products. We examined the long-term firing activity of putative DH-producing neurosecretory cells and hormonal activity of their products in male pupae that had been experienced different environmental regimens for diapause induction. Firing activity patterns of male labial cells strongly depended on diapause types of pupae: cells in a diapause-type male were active throughout the pupal period, whereas the same cells in a non-diapause-type male were usually inactive during the early two-thirds of the pupal period. A male pupa with electrically active labial cells could induce diapause eggs in a female pupa connected parabiotically to that male. The firing activity of male neurosecretory cells and hormonal action of their products are qualitatively the same as in the female previously examined. We suggest that there is no evident sexual dimorphism in the physiological and biochemical nature of neurosecretory cells producing DH and the amidated peptide DH has different functions in a male.