The inheritance of resistance to California race(s) of downy mildew in lettuce was studied in cvs. Bourguignonne, Meikoningin, Proeftuin’s Blackpool, Red Salad Bowl, Salad Trim, Ventura, and PI 164937. Resistance in cvs. Bourguignonne, Red Salad Bowl, and Salad Trim is conferred by a single dominant allele. This is the same allele found in resistant cvs. Calicel, Calmar, E-4, Imperial 410, Valrio, Valtemp, and Valverde, and is derived from resistant PI 91532. Resistance in ‘Meikoningin’ is controlled by a single dominant allele different from the one derived from PI 91532. Allelism tests indicate that the 2 alleles are independently inherited. ‘Proeftuin’s Blackpool’ and ‘Ventura’ each have 2 dominant alleles for resistance that are different from the single dominant allele derived from PI 91532. Allelism tests of ‘Proeftuin’s Blackpool’ and ‘Ventura’ indicate resistance is conferred by the same 2 dominant alleles. The 2 alleles in cvs. Proeftuin’s Blackpool or Ventura and the single allele derived from PI 91532 are independently inherited. Resistance in PI 164937 is conferred by 2 dominant alleles, one of which is the same as the single dominant allele derived from PI 91532.