Inheritance of resistance of five melon lines to two strains of Sphaerotheca fuliginea belonging to races 1 (Sf1) and 2 (Sf2) and to one strain of Erysiphe cichoracearum (Ec) have been studied. ‘PMR 45’ possesses one dominant gene controlling only Sf1. ‘WMR 29’ has one dominant gene for resistance to Sf1 and another for Sf2 and these genes seem to be linked. In line ‘PMR 5’, one dominant gene (or a group of three closely linked genes) is involved in the control of the three strains with one complementary gene for Sf1 and another one for Ec. ‘PI 124112’ has one dominant gene or two closely linked loci controlling Sf1 and Sf2 and two complementary different genes controlling Ec. ‘Nantais Oblong’ has one dominant gene controlling only Ec. A nomenclature of the genes described is proposed.