A diplod barley cultivar S upi 1 is crossed with a tetraploidHordeum bulbosum GBC141 to transfer the disease resistant traits. Eleven viable triploid F 1 plants are produced by means of embryo rescue technique. The resulting triploid hybrids are back-crossed to diploid barley, and seven BC 1 plants are obtained. One of the BC 1 plants exhibites barley yellow mosaic virus (BaYMV) resistance when grows in the diseased nursery. Isoxyme analysis of H. vulgare, H. bulbosum and their backcross hybrids are made via slab polyacrylamide gel electrophoresis technique. The primary results show that zymogram variation can be obviously found between diploid barley S upi 1 and tetraploid H. bulbosum G BC141 . A peroxidase isozyme (Rf = 0.47) from H. bulbosum is detected in the peroxidase isozyme zymogram of young roots of backcross hybrid BC 1 - 2 . This peroxidase isozyme is related to the BaYMV resistance but the linkage relation will be determined by the genetic analysis of the F 2 population in the future. The BAYMV resistant line of the backcross with isozyme maker is the important resource of barley disease-resistant breeding.