Improving maize grain yield is a major objective of breeding programs in sub–Saharan Africa. This study was conducted to evaluate the potential of two multiple stress tolerant early maturing maize populations and for improving the cross performance of elite early maturing inbred lines. Five inbred lines were crossed with two maize populations to generate 10 testcrosses using a line x tester design. The 10 testcross hybrids, the two tester populations and two commercial hybrid checks were evaluated at two locations in Nigeria in a randomized complete block design. Trait means, combining ability effects and magnitude of heterosis expressed in the crosses were estimated. Differences (P < 0.01) in performance of testcrosses, and testcross × environment interaction were observed for all measured traits. Inbred line VCML 10 combined better for grain yield with favourable ears per plant, root lodging and plant aspect ratings while TZEI 86 had the least desirable combining ability estimates for grain yield and secondary traits. Among the testcross hybrids, Early LN-W×VCML10, EWLN-POP×TZEEI-6 and EWLN-POP×TZEI-86 were the top performing combinations for grain yield. Early LN-W was the better combiner of the two populations tested. Eight of the 10 testcrosses had higher yield advantage (9.24% - 79.08%) than the better performing commercial hybrid check. The tester populations can therefore serve as sources of favourable alleles for developing better performing hybrid varieties per se as well as for inbred line extraction.