Seeds of five barley cultivars i(Clipper, C.I.3576, Proctor, Ketch and Prior) having contrasting yields and adaptation characteristics were treated with 0.04M ethyl methane sulphonate (EMS) for $ hours and populations of M2-derived treated and control lines were assessed in replicated field trials over four different sites in South Australia in the M4 generation. The treated populations of each of five cultivars gave significantly reduced mean yields over all sites and exhibited significant increases in genotypic variance, compared with the respective control populations. Similarly, the genotypic variances for heading date, plant height and seed weight were significantly increased in the treated populations. The mean heading date of treated lines of each cultivar, was shifted towards lateness whereas the mean values for height and seed weight and seed weight in the treated lines were not significantly altered except for seed weight of Prior which was significantly reduced.