The use of high-yielding varieties (HYV’s) of wheat and rice has expanded sharply in the less developed countries (LDC’s) in recent years. This report reviews the development of these varieties and statistically documents their yearly spread. Major emphasis is placed on semi-dwarf varieties (1) developed at the International Maize and Wheat Improvement Center (CIMMYT) in Mexico and the International Rice Research Institute (IRRI) in the Philippines, and/or (2) offspring of these or similar varieties developed in national breeding programs. Data cover the 12-year period from the 1965/66 crop year, when these varieties first came into use, through 1976/77. They are subject to a number of qualifications. As of 1976/77, the total HYV wheat and rice area in the non-Communist LDC’s totaled about 54.7 million hectares (135.1 million acres). Of this, about 29.4 million ha. (72.6 million acres) were wheat and 25.3 million ha. (62.5 million acres) were rice. HYV’s represented about 34.5 percent of the total wheat and rice area; HYV wheat accounted for 44.3 percent of total wheat area and HYV rice accounted for 27.5 percent of total rice area. Additional areas of HYV’s were planted in Israel, South Africa, and Taiwan, and in the Communist nations. The largest proportion of the non-Communist LDC HYV wheat and rice area in 1976/77 was located in Asia, which represented 80 percent of the total. Asia was followed by Latin America with 11 percent, the Near East with 8 percent, and Africa with less than 1 percent. India had by far the largest HYV area, representing about 52 percent of the total. Over the 12-year period from 1965/66 to 1976/77, the HYV wheat and rice area in Asia rose steadily. The rate of increase is expected to slow in the future because of both supply and demand factors.