Twenty-eight nitrogen sources (20 amino acids, 2 amide derivatives of amino acids, 4 organic nitrogen, and 2 inorganic nitrogen) were used for culture of six isolates of Diplodia natalensis and one isolate each of D. zeae, D. macrospora, Botryodiplodia theobromae, Botryosphaeria ribis, Physalospora rhodina, and a Sphaeropsis sp. Isolates were grown in synthetic liquid media and on synthetic agar media, supplemented singly with the different sources of nitrogen. Nitrogen compounds influenced mycelial growth and pigmentation, pycnidial size and orientation with respect to the substrate, presence of hairs on pycnidia, morphology of pycnidia and stromata and pycnidiospores, and exudation of the pycnidiospores. Results indicate that Diplodia and other related genera of fungi may use a wide diversity of nitrogen sources, but that the source may alter the taxonomic characters currently used to delimit this group of fungi.