A technique was developed to count chloroplasts in guard cell pairs of leaflets of anther-derived potato (Solanum phureja Juz. and Buk) plants grown in vitro to determine how they compare to chloroplast counts for similar plants grown in vivo. The mean chloroplast density in guard cells of in vitro leaflets was visualized using fluorescein diacetate (FDA) stain and observed under a microscope. A consistently higher mean was observed for in vitro than for in vivo plants but monoploid could readily be distinguished from diploid regenerants whether grown in vitro or in vivo. A rapid method of ploidy estimation based on chloroplast counts on in vitro leaflets may hasten identification of monoploids to be used for in vitro applications to genetic reconstruction of potato.