-Known a n d suspected mechanisms used by the various groups o f deep-sea fishes to locate mates and otherwise assure fertilization of gametes, and those associated with the production, development and protection of young are reviewed. These in turn are related to the reproductive demands made by the deep-sea environment. I N T R O D U C T I O N ABYSSAL fishes, like other organisms, must reproduce to survive and must adapt their reproductive habits to their environment. The deep-sea environment imposes certain problems not encountered in shoaler waters. Among them are the absence of solar light, of seasonal change, and of primary organic productivity. We propose to explore here the ways in which deep-sea fishes accommodate reproductively to this environment and to review the methods by which they solve certain biological problems common to all vertebrates. These problems include mate location and fertilization and survival of the eggs and larvae, i.e. the part of the life cycle between gonad maturity and the time at which the young is ecologically an adult. We arbitrarily take deep-sea species to be those which live as adults below 2000 m, either on the bottom or in midwater, and use as our principal list of this fauna that by M~ION GREY (1956). It will become clear that information on reproduction, eggs, and larvae of most members of this fauna is fragmentary. We consider deepsea groups to be those which have representatives which live below 2000 m. In the many instances in which reproductive information on the deep-sea forms is lacking, we have extrapolated from knowledge of those living above the 2000-m contour. We have tried to separate fact from conjecture, both in reviewing source material and in preparing our summaries, but unfortunately the conjectoral aspects of reproduction below 2000 m predominate. We will first summarize our reproductive knowledge of the major deep-sea groups and will close with comments of a more general nature. Class Chondrichthyes The sharks, skates, rays and chimaeras are represented below 2000 m by about fifteen species, many of which have broad bathymetric distributions centered above this contour (e.g., Raja bathyphyla, 676-2173 m; Centroscymnus coelolepis, 330 to below 2000 m; Harriotta raleighana, 530-2603 m). In all members of the class, *Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts. lMarinbiologisk Laboratorium, Charlottenlund Slot, Denmark. :~U.S. Fish and Wildlife Service, Washington, D.C. 569