Sterile AC hybrids between cultivated Oryza sativa (AA) and a distant wild species, O. officinalis (CC), were backcross to O. sativa. Most of the BC1 progenies were allotriploid (AAC), a few were hypotriploid. AAC progenies were again backcrossed to O. sativa. BC2 progenies consisting of disomic or aneuploid individuals were examined for the presence of O. officinalis traits. Eleven different traits from O. officinalis were identified in these progenies. Segregation data in the subsequent generations suggest that these traits are monogenic in nature. Two of these genes - for resistance to BPH and WBPH - are of value in rice improvement. The extremely low recovery of recombinant progenies is in agreement with the very low amount of pairing between A and C genomes. Because of this restricted recombination, the genotype of the recurrent parent was reconstituted after two backcrosses only. Thus, the BC2 progenies look remarkably similar to O. sativa. Most of them are stable and fertile and also interfertile with other O. sativa breeding lines. Some of the BPH-and WBPH-resistant progenies are comparable in yield to the best O. sativa parents and are being evaluated as varietal possibilities.