‘I.S.’ is a series of peach x almond clones, selected by the DCDSL “G. Scaramuzzi” of the University of Pisa, differentiated from GF 677 above all by the different degree of induced vigour. ‘Castore’ and ‘Polluce’ represent two of the most promising clones of the ‘I.S.’ series. ‘Castore’, selected as I.S.5/19, gives satisfactory results by in vitro propagation. It prefers fertile and permeable soils, whereas it is unsuitable for clay and waterlogged soils. The induced vigour (about 30% lower than GF 677) allows good growth control. Production, yield efficiency, fruit quality are also very good. Moreover, this stock adapts to poor soil where it shows good growth and yield efficiency similar to GF 677. ‘Castore’ showed a resistance to calcareous soil slightly lower than GF 677. ‘Polluce’, selected as I.S.5/8, is similar to ‘Castore’ for proliferation and rooting results by in vitro propagation. Like other peach x almond hybrids it is not suitable for wet, clay and poor drained soils, while it adapts to permeable soils, with medium or high fertility and medium-high lime content. It induces about 20% lower vigour than GF 677, and is associated with good production and high yield efficiency as well as good fruit characteristics. Overall, it becomes possible to achieve a more satisfactory and earlier vegetative balance of trees than is the case of GF 677, and show good productivity, greater yield efficiency and better fruit quality. These stocks could represent a valid alternative to GF 677 especially in high (‘Castore’) and medium-high (‘Polluce’) fertile soils, where they could allow narrow spacing in orchards and would facilitate pruning operations. In addition these clones showed a resistance to calcareous soil slightly lower than GF677. In poor soils they induce a different reduction of growth but still achieve good production.