Data of the Tygerhoek Merino flock were used to obtain halfsib heritability estimates for the components of reproduction rate within age groups as well as averaged over a number of lambing opportunities. Two separate sets of data were considered. The first set of data included progeny of all the selection group rams retained for two breeding seasons, while the second set of data included progeny of all the available rams. Reproduction traits investigated were ewes conceived/ewe mated (Ec/Em), lambs born/ewe conceived (Lb/Ec), lambs born/ewe mated (Lb/Em), the maternal component of pre-weaning mortalities/Iamb born (Ld/Lb), and lambs weaned/ewe mated (Lw/Em). The obtained heritability estimates suggested that selection for Ec/Em is unlikely to yield substantial genetic progress in the Tygerhoek Merino flock. Multiple birth rate, on the other hand, was heritable and it was contended that Lb/Ec would respond to selection, a finding which is in agreement with literature cited. The heritability estimates obtained for the maternal component of Ld/Lb were discouragingly low. Based on literature cited, however, it was concluded that the rearing ability of ewes should also be considered in a selection programme for LblEc, if the objective Is to markedly improve the composite trait of Lw/Em. Methods for the acceleration of the genetic progress in Lb/Ec and Lw/Em by the use of modern technology are proposed.