The reaction of five different Plasmopara halstedii isolates has been analysed on a range of differential genotypes. Four isolates had a similar reaction to race 1 (the European race). However one isolate had the ability to infect genotypes with no gene of resistance and also the line Rha 266 (Pl1) which is resistant to race 1. The reaction of this isolate was similar to that of the American race 2. This is the first record of this race in Morocco.