The trapping of pseudothecia carrying asci with mature ascospores of Lewia infectoria (teleomorph of Alternaria infectoria) from wheat stubble under natural field conditions in Buenos Aires Province, Argentina, is reported for the first time. The production of mature pseudothecia in culture is also reported. Monosporic isolates of A. infectoria, obtained from infected wheat plants in Argentina, produced conidia within a week and ascomata with fully mature ascospores within 7 months when stored on slants of PCA at 4°C in darkness. The anamorph exhibited the sporulation pattern of Alternaria infectoria species-group, and was identified by its axenic colony morphology and the prominence of its secondary conidiophore structure. Critical examination of the teleomorph revealed it to be Lewia infectoria. The presence of the teleomorph has implications in the long-distance dispersal of A. infectoria and on resistance breeding programs. This is the first confirmed report of the sexual stage of A. infectoria in Argentina.