Information about combining ability is important for making breeding strategies. A nine parent diallel excluding reciprocals was formed for the inbreds developed by the Maize Programme at NARC, Islamabad. These inbreds were derived from material from temperature, subtropical and tropical ecologies and their combining ability effects were estimated for 11 biometric traits. GCA effects were highly significant for all the traits under study, but SCA effects were less significant in certain cases suggesting predominance of additive genes. High GCA effects for grain yield were observed in the temperature material i.e. QPM-1 (0.168), QPM-3 (0.169) and QPM-5 (0.485), while SCA effects were remarkable for hybrids QPM-3 x NCML-1078 (0.890), NCML-1071 x NCML-1084 (0.878) and NCML-1082 x NCML-1083 (0.831). Temperature material also gave high GCA effects for striking characters contributing towards high grain yield i.e. plant and ear heights, leaf area, ears plant-1, ear weight and kernels row-1. Tropical inbreds gave eminent GCA effects for days to pollen shedding, ear weight and grain moisture at harvest. Considering its negative GCA and SCA effects for days to pollen shedding, subtropical material was marked as a valuable source for inducing earliness.