Genetic variability for resistance to Alternaria leaf spot disease (Alternaria helianthi) can be induced by radiation or chemical mutagens. The objec tives of this study were to create genetic variability in cultivated sunflower and to select lines resistant to Alternaria leaf spot. In the first experiment, sunflower seeds of the genotype HA BR 104 were irradiated with 150 and 165 Gy of gamma rays. Seeds were sown in the field at the Embrapa Soybean experimental station, in Londrina, PR, Brazil and M1 plants were harvested in bulk. M2 ,M3 and M4 plants were screened for disease resistance under natural infection in the field. Plants were evaluated for Alternaria leaf spot symptoms, using a diagrammatic scale from 0 (no symptoms) to 5 (maximum infection). Before flowering, plants showing no symptoms of Alternaria leaf spot (grade 0) or less than 5% diseased leaf area (grade 1) were bagged for self-pollination. Self-pollinated plants and open-pollinated plants from 150 Gy and 165 Gy populations with no or mild disease symptoms were selected. In the second experiment, sunflower seeds of the genotypes HA 300 and HA BR 104 were treated with ethyl methanesulfonate (EMS) at 0.015 mol dm-3. Selected M2 and M3 were screened for disease resistance in the field. From the EMS treatment, 300 M3 plants with no disease were recovered. All these lines will be tested for combining ability. The best lines will be used for hybrid production.