The Plus-Hybrid system, the cultivation of a transgenic cytoplasmic male sterile (CMS) hybrid and a second unrelated hybrid as pollen donor, has been proposed by us as a method for biocontainment of GM transgenic pollen. Private companies are able right now to provide suitable CMS hybrids right now; as the grain yield is increased by combining CMS and Xenia effects, the acceptance of this containment strategy is improved. At present, we aim at defining optimal hybrid combinations leading to a higher expression of the Plus-Hybrid effect. Field experiments were conducted in four countries, Switzerland, France, Germany and Bulgaria with a set of modern European hybrids from actual variety lists. The average grain yields of Plus-Hybrids were indeed higher, some very suitable Plus-Hybrid combinations were identified that should enable breeders to offer Bt-maize within this biocontainment system soon.