Twenty-three species of anophelines have been reported as hosts of Microsporidea, principally Thelohania spp., but only 3 species, 2 of Nosema and 1 of Pleistophora (all exotic) are readily transmitted perorally in the laboratory; the same 3 species have also caused outbreaks of microsporidiosis in many anopheline colonies. Sixteen species of anophelines have been reported as hosts of nematodes, but only 3 are parasitized in the adult stage; the cycles of the Romanomermis and Gastromermis spp. that emerge from larvae and the nematodes that emerge from adults are very different. Viruses such as the mosquito iridescent virus, cytoplasmic polyhedrosis viruses of the hypodermal and gut cells, and a nuclear polyhedrosis virus are reported only from culicines, but 2 probable cytoplasmic polyhedrosis viruses, one in the hypodermal cells and the other in the gut cells, are reported from larvae of Anopheles crucians Wiedemann.