Diploid hybrids in the Bromopsis section of Bromus were, in general, morphologically intermediate, but instances of dominance and heterosis occurred. F1 tetraploid hybrids between B. ciliatus and B. frondosus segregated into dwarf, semi-dwarf, and normal types. Diploid hybrids showed mean bivalent frequencies of 6.50 to 6.79 per MI cell and little irregularity in AI and quartet stages. Mean bivalent frequencies of 12.33 to 12.81 and moderate frequencies of univalents, trivalents, and quadrivalents occurred in MI cells of F1 tetraploid hybrids. Diploid hybrids were highly sterile, but showed slight fertility as seed parents in backcrosses. Tetraploid hybrids exhibited low fertility under open-pollination.