The present study deals with the location of the vitellogenesis inhibiting hormone (VIH)-producing cells in the eyestalk of the lobsterHomarus americanus.In the present study, the neurosecretory pathways of VIH in Homarus, have been described immunocytochemically by use of a mouse serum againstHomarusVIH. The location of the VIH cells was compared with the location of the crustacean hyperglycemic hormone (CHH) cells visualized by a rabbit serum raised against CHH of the crayfishAstacus leptodactylus.Immunocytochemical detection procedures, both at the light and electron microscopic level, revealed frequent but not complete co-localization of VIH and CHH in a variable number of the same group of perikarya. In the sinus gland, both neuropeptides were mostly demonstrated in distinct axonal endings characterized by different granule types. Postulations on the biosynthesis of these factors and suggestions concerning the processing of both neurohormones have been made.