This paper records a preliminary investigation of variation in N ectria stenospora Berk. & Br., a species which produces both sexual and asexual spores in culture. The cultural characteristics of the species and methods for isolation of single ascospores and conidia are described. Staining reveals that, all cells of the frequently anastomosing mycelium are uninucleate. Two types of variation are described, one being a gene-controlled variation in colony colour, the other a cytoplasmically controlled variation in colony texture. Certain strains are shown to be self sterile, others self fertile although preferentially outbreeding.