The effects of epidemics of leaf rust (Puccinia hordei Otth.) on grain size and yield of some commercial Australian barley cultivars were determined in 3 field experiments at or near Toowoomba in 1985, 1989 and 1990. Yield was reduced by 38% for the highly susceptible cultivar, Gus, in a mild to moderate epidemic in 1985; cvv. Prior, Schooner, Clipper, Lara and Stirling lost between 10 and 20% yield and cvv. Corvette and Grimmett were unaffected. In a mild to moderate epidemic in 1989, leaf rust reduced the yield of Gus by 40%, and of Grimmett and Clipper by 17 and 12%, respectively, while Prior and Corvette were unaffected. In a moderate to severe epidemic in 1990, yield losses were 62% in Gus, 26% in Grimmett, 31% in Skiff and 14% in the slow-rusting cultivar, Athos. No losses were detected for Corvette or the slow-rusting cultivar, Koru. Loss of yield was largely attributable to reduction in grain size.