Pyrenophora graminea, the causal agent of leaf stripe of barley, is an economically important disease with a worldwide distribution. To examine the inheritance of virulence in this fungus, a cross was made between two isolates that differed widely in their DNA and virulence. Of the 70 progeny tested, 36 exhibited high virulence and 34 exhibited low virulence on the barley cultivar Furat1. The data support a model in which a single, major gene controls virulence in P. graminea (1 : 1 ratio; X² = 0.72, P = 36.3). This information will now allow for a map-based cloning approach to identify the gene.