In order to transfer useful genes of Hordeum californicum into common wheat (Triticum aestivum L.), the T. aestivum c.v. Chinese Spring (CS)-H. californicum amphiploid was crossed to CS, and its backcrossing and self-fertilized progenies were analyzed by morphological observation, cytological, biochemical and molecular marker techniques. Alien addition lines with two H. californicum chromosomes were identified and their genetic constitution was characterized. STS-PCR analysis using chromosome 2B specific markers indicated that chromosome H3 of H. californicum belongs to homologous group 2, and was thus designated 2H. SDS-PAGE showed that chromosome H2 of H. californicum belongs to homologous group 5, and was designated 5H. The CS-H. californicum amphiploid and the chromosome addition lines (DA2H and MA5H) identified were evaluated for powdery mildew (Erysiphe graminis f. sp. triticii) resistance in field. The preliminary results indicated that the amphiploid showed higher powdery mildew resistance than CS. However, chromosome addition lines DA2H and MA5H were highly susceptible to powdery mildew, indicating that major powdery mildew resistant genes of H. californicum should be located on chromosomes other than 2H and 5H.