Dynamics of genetic load in aboriginal population of the Turkmen SSR was studied using two approaches to calculate "lethal" equivalents. Intensity and structure of natural selection were measured using the Crow's index and its components. All statistics indicated were determined using the data obtained in Ashkhabad city and in two rural populations of Ashkhabad region (Yasman and Nokhur) within the time interval prior to 60s and after 70s. The results obtained made it possible to subdivide the populations under study into three different groups according to different stages of demographic process: 1) urbanized population; 2) rural (transient) population; 3) "relict" rural population.