A total of twenty experimental hybrids of sunflower were tested for their resistance to three pathogenic races of Plasmopara hrrlstedi. The experiments were conducted in a plastic house where WSl-inoculated seedlings were grown and evaluated for disease reactions twice in a 4-week period. As control, a universal susceptible (cv. GK-70) and a few (both compatible and incompatible) differential lines were used to ascertain that the reaction to the races was correct. All the sunflowers tested under the plastic tunnel were resistant to race I, with only two entries showing some infection. As for race 3 resistance, they varied greatly. Three entries exhibited good resistance (7o infection <20), two others were moderately resistant (20- 50% infection), and fifteen showed susceptibility. A similar segregation was found with race 4 resistance, where, besides three resistant entries and I I susceptible ones, there were six hybrids with intermediate reaction (7o infection 20-50). The results obtained suggest that sunflowers with resistance to downy mildew races 3 and 4 are available and mav be released soon.