An in vitro screen of 83 isolates of coprophilous fungi revealed that many of them were capable of stimulating growth of Sphaeronaemella fimicola at a distance. When in direct contact with S. fimicola, many (excluding the Zygomycotina) also stimulated the production of perithecia. Species of Coniochaeta, Ryparobius, Thelebolus and Trichobolus were the strongest inducers. These and related genera were also associated with perithecia of S. fimicola on dung collected from the field. Hyphae of many of the strong perithecium inducers and a few non-inducing species were parasitized by necrotrophic intrahyphal growth of S. fimicola. Perithecium formation was stimulated even when parasitism was prevented by separation of growing mycelia of Ryparobius pachyascus and S. fimicola by Cellophane. In contrast, prior growth and removal of R. pachyascus followed by inoculation with S. fimicola caused enhanced growth and asexual reproduction without concomitant perithecium formation.