Ten species of Hypomyces (Ascomycotina, Hypocreales, Hypocreaceae) occur on members of the Boletaceae (Basidiomycotina, Agaricales). Five new species, viz. H. badius, H. boletiphagus, H. chlorinigenus, H. melanochlorus, and H. microspermus are described. One new combination, H. completus, is made. All species have a proven (five species) or associated (five species) anamorph referable to Sepedonium. The five species grown in culture from isolated ascospores produced hyphomycetous synanamorphs, and synanamorphs have been detected in collections of the other five species. The boleticolous species ofHypomyces (Fries) L.-R. Tulasne (1860) have the features typical of the Hypocreales, Hypocreaceae as given by Rogerson (1970). These are soft, fleshy, globose, obovoid to obpyriform, typically papillate, brightly colored, periphysate perithecia, a basal hymenium of apical paraphyses in early stages of development and a centrum filled with unitunicate asci at maturity. Distinctive characteristics of Hypomyces include: a well developed subiculum; perithecia with a wall composed of a single region of cells with cells of papilla arranged in diverging files, the terminal cells of which are usually en? larged and clavate becoming progressively narrower toward the ostiolar canal and there merging with the periphyses; cylindrical non-amyloid, 8-spored asci with an apical pore; hyaline, fusiform, typically verrucose and often apiculate ascospores that are uniseriately arranged in asci; and a fungicolous habit. Although presence of a well-developed subiculum is a typical feature of species of Hypomyces, considerable variation in density, texture, color, etc, occurs within and between species. Often, when perithecia are mature, the subiculum is not discernible. In the bo? leticolous species the subiculum is at first white and loose, then it becomes dense, cottony, and colored; it does not become compacted and more or less stromatic as it does in some non-boleti