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There is an increasing need for new means of population control from the simplest organisms up to the larger mammalian species (include man if you wish.) A number of interesting and promising leads, such as environmental manipulation, introduction of predators, diseases, parasites, etc., and particularly antifertility agents, have been proposed for some time, but research into the latter approach in mammal control is quite recent and limited. The use of toxic agents has long been the principal method of vertebrate population con¬trol, but the potential for the use of antiferti1ity agents to suppress reproduction may provide an important advancement. I wish I could tell you that all we have to do is to develop or discover the right antiferti1ity agent and we have the problem solved. Unfortunately this is far from the truth. Based on present knowledge of antifertility agents in vertebrate pest control, it appears that we will need a variety of agents and even more im¬portant, a wide variety of techniques of application plus the detailed knowledge of proper timing, dosage, and dispersal of bait for effective results. In many instances, the problems of application far outweigh the development of a suitable drug. At present it appears that the greatest potential lies with animals that breed once a year and secondly with birds such as pigeons. When it comes to rodents, a major problem arises; a temporary antiferti1ity agent will have to be continuously available to block reproduction throughout the year or else permanent sterility agents wi11 be needed which are apt to be so toxic they provide little advantage over a poison.