The field reactions of 19 bread wheat lines and three durum wheat lines to Puccinia triticina showed that the bread wheat lines were susceptible to moderately susceptible while that of three durum wheat lines were resistant, and moderately resistant. The seedling reactions of bread and durum lines against three races, FHTT, PHTT, and PRTT showed that bread lines were susceptible to all the races while durum lines were resistant. All of the tested durum lines were found to be promising for wheat breeding studies carried out against leaf or brown rust of wheat. Introduction Leaf or brown rust, caused by Puccinia triticina Eriks., (syn. P. recondita Rob. Ex Desm. f. sp. tritici Eriks. and Henn.), is one of the most severe diseases of wheat (Triticum spp.) in many wheat growing regions of the world. Yield losses due to leaf rust on wheat cultivars vary from 5 to 15% (Samborski 1985) or more, depending on the level of resistance, and stages of crop maturity when initial infection occurs (Liu and Kolmer 1997, Kolmer 2001). In some countries, yield losses up to 40 -50% have been reported (Marshall 1988). Use of resistant cultivars has been preferred to limit losses from rusts for many years (McVey and Long 1993). The use of resistant cultivars is the most effective and environmentally friendly way of protecting them against leaf rust (Singh et al. 2001, Wamishe and Milus 2004, Martinez et al. 2005). The objective of present study was to determine the reaction of wheat breeding lines in Turkey to leaf rust and their potential for use in developing resistant cultivars.