Various fixation methods were used to study conidium ontogeny in Stachybotrys atra Corda. Phialides arise by subterminal branching of the conidiophore. The first spore originates from the inner layer of the phialide tip, breaking the other wall layers. Thereafter spores are produced from the inside of the phialide neck where new wall layers are formed. Spores are cut off from the phialide by a septum and this splits to release the spore. As spore production ceases the phialide neck becomes plugged, the basal septum of the phialide becomes plugged and the cytoplasm vacuolates. Spores have a rough, pigmented two-layered wall and the usual organelles.