Interest in plant sources of prototypic contraceptive compounds is evidenced by numerous investigations and research projects. We suggest that the success rates of programs devised to evaluate pharmacological effects of traditionally employed contraceptives would be increased if native concepts of conception/contraception were taken into account. If ethnomedical and ethnopharmacological data are not carefully analysed, selection of plants to be evaluated will include those with little cross-cultural application. Kayapo concepts of menstruation, fertility, and contraception are presented, uses of related plants in culturally different groups are also analysed in order to indicate promising fertility-regulating plants used by the Kayapo.