We review recent literature to address the question to what extent are nectarivorous and frugivorous mammals legitimate, efficient, and effective dispersers of pollen and seeds of plants? There is growing observational and experimental evidence to indicate that mammals are legitimate dispersers of the pollen and seeds of many species of plants in a wide variety of habitats. Current evidence indicates, however, that mammals often ''waste'' much pollen or many seeds and, hence, are relatively inefficient mutualists. Experimental work indicates that, despite their low efficiency, mammals are the most effective pollinators or dispersers, hence have a positive effect on reproductive success, of many plants in tropical and arid habitats. The genetic consequences of mammalian pollination and seed dispersal are just beginning to be investigated.