Subterranean clover Trifolium subterraneum L has been an important pasture legume in southern Australia for some fifty years and large areas are sown to it in New South Wales, Victoria, South “Australia, western Australia and Tasmania. Attack by the rust Urogyces trifolii (Hedw) Lev. was first reported in N.S.W. in 1929 from a pasture on the central coast and since then the disease has become recognised as one of the most serious attacking subterranean clover, particularly in N.S.W. coastal and irrigation districts. In these areas rust attack could become a factor limiting the use of subterranean clover, and therefore in 1954 the present study was commenced to investigate the problem of rust-susceptibility of the clever and the practicability of breeding rust-resistant strains.