Colletotrichum dematium is the cause of a new fungal stem disease on cowpea in South Africa. The pre-penetration and infection process of this fungus on cowpea stems was studied by light microscopy and SEM. Conidia began germinating at 6 h post inoculation (hpi), forming appressoria directly or at the ends of germ-tubes. By 14 hpi appressoria had melanized and direct penetration of host tissue had begun. At 20 hpi infection vesicles formed in epidermal cells. Thick, knotted primary hyphae formed from these vesicles and entered adjacent cells. At ±40 hpi C. dematium produced secondary hyphae which were highly branched, and grew extensively inter- and intracellularly. After approximately 48 hpi light brown lesions appeared on the stem, associated with the invasion of secondary hyphae into cells and cell necrosis. Acervuli with one or two melanized setae were visible on lesions by 70 hpi.