Diploid, triploid, tetraploid, and hexaploid alfalfa plants had 9.2, 9.4, 12.8. and 15.2 chloroplasts per pair of stomatul guard cells, respectively. Plants at the four ploidy levels could be separated into three groups as early as the seedling stage of growth. The technique could be used to screen alfalfa populations for plants with desired ploidy levels, and restrict chromosome counting to verification of selected plants.