Five new or locally unexploitedLrgenes were evaluated as sources of resistance to leaf rust (Puccinia recon- ditaRob. ex Desm. f. sp.tritici) of wheat (Triticum aestivumL.) in South Africa. The expression ofLr36, Lr41andLr42, as well as the provisionally named genes'Lr39and‘Lr40’, their reaction to different temperatures and inheritance in two South African wheat cultivars were determined.Lr36in line C78.10 was more effective at higher temperatures whereasLr39(line KS86WGRC02) andLr40(line KS89WGRC07) conferred lower infection types at 15°C than at 25°C. Except for more pronounced flecking at 15°C, temperature had no detectable effect on the expression ofLr41in line KS90WGRC10. An interaction between temperature and pathotype showed thatLr42in line KS91WGRC11 was less effective to certain pathotypes at lower temperatures. According to seedling infection types in the F2and BC2F1,Lr36, Lr39andLr40were inherited as partially dominant genes in Karee and Palmiet. With these backgrounds,Lr39andLr40produced similar infection types.Lr41was partially dominant in Karee, but similar, highly resistant infection types suggested complete dominance in Palmiet.Lr42was partially dominant to pathotype UVPrt13 in Palmiet, but recessive to UVPrt9 in Karee. The results obtained in this study provided information for the establishment of reliable selection criteria forLrgene management during wheat leaf rust resistance breeding.