The variability of human chromosomal Q-heterochromatin regions (Q-HR) was studied in 385 newcomers well adapted to the extreme environmental conditions of Pamir and Tien-Shan, as well as in 284 representatives of the native population of these regions. Newcomers were found to represent a highly homogeneous group as regards all the quantitative characteristics of Q-HR variability, but at the same time they differed significantly from both native residents and individuals of similar nationality (Russians) living permanently at low altitude. Differences between these three groups in the amount of Q-HRs in their genome are discussed as evidence in favour of the hypothesis of the possible selective value of chromosomal Q-heterochromatin material in human adaptation to extreme environmental high-altitude conditions.