Nineteen selected 85 white maize lines derived from the wide genetic base population Tepalicinco (Tep#5). from SIMMYT, were topcrossed to each of two commercial inbred testers, i.e. so 7 and Grn 22 in 2003 summer season. The resultant 38 testcrosses Were evaluated in 2004 growing season at Gemmeiza and Mallawy Agricultural Research Stations. for grain yield and its components as well as days to 50% silking. Results obtained revealed that the additive component of gene action had the major role in the inheritance of the most studied traits compared with the non-additive ones. Highly significant differences were detected among the tested lines and their testers. as well as. the interaction between them. The tested lines L-1 L-5. L-8, L-9, L44. L-1? and L-19 manifested the best general combining ability (GOA) effects based on the combined analysis. Parental lines L-1. L-2. and L-18 and their testcrosses were earlier than the check hybrids SC 10 and SC 124. Moreover single crosses of L-1 and L-2 with so 7 significantly outyielded the commercial check hybrid SC 124. Meanwhile. the inbred tester Sd T crossed to the tested lines L-3. L-4 L-5. L-B, L-9. L-13, L-14. L-17 and L-19 produced the best single crosses which significantly outyielded the check hybrid SC 124 with an average increase from 3.4 to 8.0 ard/fad. Furthermore, the most outstanding crosses. i.e. L-B x Sd 7, L-14 x Sd 7 L-19 x so 7. and L-1 x Sd 7 (37.2. 36.5. 36.3 and 35.9 ardlfad. respectively outyielded the best commercial check hybrid SC 10 (35.4 ardlfad) by 1.8, 1.1 , 0.9 and 0.5 ardlfad, respectively.