The genetically significant dose was initially defined by UNSCEAR in 1958. The National Radiological Protection Board (NRPB) derived a formula from this definition as shown in the NRPB Report, NRPB-R106. It combines the frequency of radiological examinations obtained during the country-wide survey and estimates of gonadal doses for different examination types, together with population and child expectancy data. The task was set to find a model in order to draw the best representative sample of the population, and it was determined in a unique way, namely the so-called Dollar Unit Sampling method. A sample of 27 institutions out of a possible 292 (9%) was drawn. The GSD for the total South African population was calculated, using the above-mentioned formula, as 95 microGy. The breakdown of the genetically significant dose for the various South African race groups was Asian--229 microGy; black--67 microGy; people of color (mixed race)--112 microGy; and white--463 microGy.