Cucumber (Cucumis sativus) is a major glasshouse crop in the Netherlands. Although breeding has resulted in cultivars resistant to many diseases, the crop is still threatened by a number of diseases such as Cucumber Green Mottle Mosaic Virus and powdery mildew (Sphaerotheca fuliginea). Certain wild Cucumis species harbour dominant monogenic resistances against these diseases. Crossing of these wild species with cucumber, however, is inhibited by strong crossing barriers [1]. Transfer of the genes responsible for the resistances may be provided for by somatic hybridization. To realise this, methods for protoplast culture and plant regeneration must be developed.