The successful development and cultivation of hybrid rice in China in 1976 encouraged IRRI scientists and collaborating countries to intensify this research in 1980. Because the Chinese hybrids and parental lines were not adapted to the tropics, IRRI began collaborating with several tropical rice-growing countries to develop suitable parental lines and hybrids. By 1989, IRRI developed two commercially usable cytoplasmic male sterile (CMS) lines that, when combined with easily available restorers among elite tropical indica rice cultivars, produced hundreds of experimental rice hybrids. Some of these yielded about 1 t ha-1 more than inbred checks in national trials under irrigated conditions. By 1994, India, Vietnam, and the Philippines had released some promising rice hybrids for commercial cultivation by farmers.