Abstract. For the purposes of preliminary evaluation of the combining ability for grain yield of 12 mutant maize lines a top cross method for early testing and the mathematical model of Savchenko(1993) for analysis of the general combining ability and specific combining ability of these lines are used. Mutant lines are tested by three testers that have proven high general combining ability. For the purposes of evaluation of the productive abilities of the received top crosses at the experimental filed of Maize Institute,Knezha three preliminary varietal experiments are carried out by using agro technique accepted for the region. As a result of the committed experimental workand the analysis performed under the method of Savchenkoit is established that the lines ХМ 42-7-1*-1, ХМ 34-1-1*- 1 and ХМ 33-4-4-1 have the highest generalcombining ability. They can be used as components for obtaining synthetics with high yields or as testers in analyzing crosses for determining the general combining ability at earlier stages of the selection process. Specified lines with high specific combining ability – ХМ 4-1-1-1, ХМ 31-1-3*-1, ХМ 44-6-2*-1, ХМ 34-1-1*-1 and ХМ 3-5-1-1 are appropriate to be included in the combination for obtaining hybrids with high yields. Two mutant lines of the spectrum – ХМ 33-4-4-1 and ХМ 42-7-1*-1, have both high general combining ability and specific combiningability. They can be used in both selection directions.