SUMMARY In this investigation of Helminthosporium victoriae routine techniques of electron microscopy were used, except for a slightly modified potassium permanganate fixative. The cell wall consisted of two parts : an outer thin electron-dense layer and an inner broader electron-lucid fibrillar layer. A thin plasma membrane was contiguous with the inner layer of the cell wall. The sparse endoplasmic reticulum ramified throughout the cyto- plasm in a sinuous fashion. Mitochondria displayed classical structure and were ubiquitous in distribution. Glycogen and lipids were constantly occurring inclusions. Simple septa1 pores were present. Large vacuoles with tonoplasts and also numerous smaller vesicles were seen. Hyphae were often multi-nucleate.