An electron microscope study has been done on the structure of microconidia and stroma of Sclerotinia sclerotiorum. The microconidia showed the usual cell organelles already described for other species of this genus, e.g. a large nucleus and large lipid body, a few mitochondria and sparse endoplasmic reticulum. The stromatal ultrastructure presented hyphae with a rich content in lipid bodies and storage vacuoles as food reserve. Simple septa with plugged pores were occasionally seen. Although the existence of two kinds of hyphae, one with abundant food materials and the other type with a degenerated aspect, both hyphae showed a similar thickness in their cell walls approximately 0.2 μ, and the diameter of these hyphae was 1.5–3 μ.