Over the past decade entomopathogenic fungi in relation to flies in livestock production have been studied extensively in Denmark. Main focus has been given to natural occurrence, epizootiology and host specificity of different species of Entomophthorales, while studies of mitosporic fungi (Hyphomycetes) have included the control potential notably against the stable fly, Stomoxys calcitrans, as well as compatibility with other natural enemies used for fly control. This presentation provides an overview of the knowledge gained, with special emphasis on recent findings of Entomophthora muscae infection in populations of S. calcitrans. Up to 30% of the flies succumbed to fungal infection. This strain of E. muscae was found to be adapted to stable flies, although some infection could be obtained also in Musca domestica.