Abstract: Methods and apparatus for the introduction of foreign substances, such as recombinant DNA, into living cell interiors is disclosed. The desired substance to be introduced is dissolved or suspended in water or another suitable liquid to form a solution which is then nebulized and frozen to produce ice particles. These ice particles are accelerated toward and impact upon a target tissue where some of the particles impregnate at least some cells in the target tissue without killing the cells. Following impregnation, the ice particles melt, leaving behind the desired substance in the protoplasm of the bombarded cell.