Mutation experiments require careful selection of a mutagen with characteristics suited to the tissue source and mutagenesis objective, and an appropriate treatment regime. The objectives of the present investigation were:-to compare the ability of immature embryos to initiate calluses and calluses derived from immature embryos to survive and grow after being treated with ethyl methanesulfonate (EMS) doses of 0.2, 0.4, 0.8, 1.2, and 1.6% (v/v) and-to compare these results with those published for seed mutagenesis. To determine if the response of tissue source to EMS treatment varied with genotype, tissues from two spring wheat cultivars, 'Angus' and 'Pavon 76', were used. The combined analysis of variance detected highly significant differences (p---0.01) among doses. The higher the dose, the lower the tissue survival in each tissue source. No significant differences were detected between cultivars, tissue sources, in the cultivar by dose interaction, tissue source by dose interaction, tissue source by cultivar interaction, or tissue source by cultivar by dose interaction. Hence, both cultivars and tissue sources responded similarly to EMS doses. The predicted LD20 are 0.35% +--0.08% for the immature embryo treatment, and 0.36% + 0.10% for the callus treatment. The predicted LDs0 are 0.82% +-0.13% for the immature embryo treatment, and 0.77%,+ 0.13% for the callus treatment. These results were very similar to published results for seed mutagenesis, hence seed mutagenesis research may be applicable to immature embryo and callus mutagenesis.