A method for stably transforming barley from mature barley seeds as starting material is disclosed. The method involves germinating mature barley seeds until early shoot development occurs, exposing scutellar or embryo tissue cells on the embryo side of germinated seeds, and introducing foreign DNA into the cells. The cells are initially grown under conditions that allow expression of a selectable marker introduced with the foreign DNA, then on a callus-growth medium effective to suppress callus formation in the absence of the selectable marker. Successfully transformed calli can be cultured in suspension to obtain a desired foreign protein, or regenerated into plants, to obtain the foreign protein from the transformed plants, e.g., germinated seeds.