The perfect state of Septoria trltici Rob. apud Desm. (Mycosphaerella graminicola) (Fuckel) Schoeter was isolated from foliar lessions of mature wheat plants (Buck Poncho cv.) at J.Hirschhorn Experimental Station of Buenos Aires Province. This is the first report of the telemorph of Septoria tritici in Argentine. All the diseases samples that were suspected to be Mycosphaerella graminicola were brought to the laboratory and optic and scanning microscopic examination were made to identify the pathogen. Ascocarps, asci and ascospores were descripted and measured. The fungus isolated were obtained by descharging ascospores in culture media. The morphology, colour and sporulation of the colony were studied. The ascospore germination process were observed through Fitzgerald and Cooke method. The above mentioned microscopic observations of the fungus were close to the original description for M. graminicola (Fuckel) Schroeter, the ascogenous state of S. tritici Hob. apud Desm. Since the ascogenous state of this fungus has already been reported in neighbour countries (Chile and Brazil) its importance in the epidemiology of the disease is being intensively studied.