Colchicine has usually been applied to sterile clones of interspecific grass hybrids to restore fertility. However, when hybrids are partially fertile, colchicine can be applied to germinating seedlings. Four populations of Basin wildrye (Leymus cinereus) X beardless wildrye (L. triticoides) were treated with a 0.2% colchicine solution to double chromosome number from 4x=28 to 8x=56. Doubling percentage was 28, 33, 42, and 44% of all root-tips examined for the four populations. When plants without doubled sectors were discarded, doubling percentage increased to 56, 68, 78, and 78%. Plants with doubled sectors have been placed in crossing blocks to generate octoploid progeny. Octoploids identified through root-tip chromosome counts will be intercrossed to generate 8x populations