Previous studies have suggested that the hematocrit and hemoglobin values in Himalayan natives (Sherpas) are lower than those of Andean natives (Quechua Indians) living at the same altitude, perhaps because of genetic differences. To study these populations further, we selected healthy male subjects in Ollame, Chile (n=29, age=27.3 -+ 15.9 years), and in Khunde, Nepal (n=30, age=24.7 2 13.8 years). Both of these villages are located at 3,700 m above sea level. Hematologic measurements confirmed lower hematocrit values in Nepal (48.4 k 1 4.5%) than in Chile (52.2 2 1 4.6%) (P<0.003). When subjects were matched for hematocrit, erythropoietin concentrations in Chile were higher than in Nepal (RO.01).