ABSTRACTThree new species ofSmittium(Harpellales) are described from the hindguts of dipteran larvae collected near Gothic, Colorado.Smittium perforatum, from Chironomidae, is the second species of the genus known to penetrate the gut cuticle.Smittium coloradensewas dissected from chironomids and possibly from simuliids. Tipulid larvae are the hosts forS. tipulidarum, which was cultured axenically. The range ofS. pusillumandS. typhellumis extended from France to the United States.