To study the effect of γ-ray treatment on donorand derived somatic hybrids, we carried out γ-ray donor treatment experiments with a wide range of γ-ray dosages and asymmetric somatic hybridization between protoplasts of wheat (Triticum aestivum L. Jinan 177) and protoplasts of Haynaldia villosa Schur. treated with different dosages of γ-rays (40, 60 and 80 Gy, respectively). We first screened the putative hybrids by isozyme analysis, followed by characterization of nuclear and organellar genome composition of the hybrids. Genomic in situ hybridization on mitotic metaphases demonstrated that the donor chromosome elimination in the hybrids increased with increased γ-ray dosage. Intergenomic chromosome recombination/translocations were observed in the hybrids from different dosages of γ-rays. PCR amplification of 5S rDNA spacer sequences showed that only some of the regenerated hybrid clones inherited donor 5S rDNA sequences, suggesting that the donor DNA was also eliminated randomly. Restriction fragment length polymorphism analysis using mitochondrion (mt) and chloroplast (cp) genespecific probes showed that the hybrid calli contained mt genomes of both parents and the cp genome of only one of the parents. Recombinations between parental mt as well as cp genes were found in the hybrid clones. Furthermore, development of the hybrid clones was dependent on the γ-ray dosage used for the donor treatment. Regenerated plants were only obtained from fusion combinations of low (40 Gy) and intermediate (60 Gy) dose irradiation. The possible role and significance of γ-rays on the introgression of small segments of donor chromosomes to the receptor is discussed.