Neurohypophysial hormones have been investigated in both the Australian lungfish (Follett & Heller, 1963, 1964) and the African lungfish (Follett & Heller, 1962, 1963, 1964; Sawyer & van Dyke, 1963). The African lungfishes (Protopterus aethiopicus) used by Follett & Heller (1964) had been caught in Lake Victoria, Uganda, and their glands contained two hormones with the properties of arginine vasotocin (AVT) and 8-isoleucine oxytocin as did the pituitaries of the Australian lungfish (Neoceratodus forsteri) examined at the same time. Sawyer & van Dyke (1963) used Protopterus aethiopicus which came from a different lake (Lake George, Uganda) and glands from these fishes contained AVT and oxytocin, although in another batch of glands Sawyer (personal communication) found evidence for the presence of 8-isoleucine oxytocin. Both groups of workers, however, suggested the possibility of a mixture of both the oxytocin-like peptides in the glands they had analysed. The present work was undertaken to