Freeze-etching and chemical fixation techniques were used to study exogenously dormant spores, spore germination, hyphae and conidiophores of Alternaria brassicicola (Schw.) Wiltshire. Dormant spores have very thick, heavily pigmented, mclanized walls with plugged septal pores. The small amounts of endoplasmic reticulum and the few mitochondria lie near the plasmalemma. The germ-tube walls arise from the inner layers of the spore walls; lomasomes and endoplasmic reticulum vesicles are probably concerned with this wall formation. During germination mitochondria and ribosomes increase in numbers, first in the germinating cell and then in the germ tube. As the hyphae age they produce lipid droplets and vacuoles; the latter finally fill most of the cell as the cytoplasm degenerates. Conidiophores have a similar structure to mature hyphae except that they have, after spore production, a pore in the tip and an annulus.