Sunflower (Heltanthus annuus L.) can be affected by leaf blight and stem spot disease caused by Alternaria helianthi. Genotypes with genetic resistance to this disease are highly desirable for reducing yield losses. The reaction of 28 sunflower genotypes to Alternaria leaf spot disease was evaluated in the state of Paraná, Brazil, during the 1995-96 and 1996-97 growing seasons. Disease occurrence, under natural conditions, was evaluated at the flowering stage with reference to a diagrammatic scale of severity, varying from 0 to 5 according to the area of diseased leaf tissue. High Alternaria disease intensity was observed in eight field trials. The genotypes Contiflor 3, Contiflor 15 and Cargill 9401 showed an intermediate level of resistance to the Alternaria disease.