Drought and low nitrogen stress, the major abiotic stresses limiting maize production in the tropical and subtropical developing countries, frequently occur together causing significant decline in maize production. Through several years of breeding maize for stress tolerance, the International Maize and Wheat Improvement Center (CIMMYT) has produced inbred lines tolerant to the two major stresses. The objectives of this study were to (i) investigate the combining ability of inbreds and hybrids, (ii) assess genotype x environment interaction across stress conditions and testing locations and (iii) estimate heterosis under the different stresses. Fifteen inbred lines of tropical and subtropical origins with a range of response to abiotic stresses were crossed in a diallel mating design. The resulting 105 hybrids were evaluated under well-watered, drought stressed, and low nitrogen conditions in three countries in a replicated alpha-lattice design. Measurements for anthesis date, silking date, anthesis-silking interval, ears per plant, and grain yield were taken in each environment. General and specific combining abilities effects were estimated following Griffing's (1956) diallel analysis. Both GCA and SCA mean squares across environments were significant for all the traits. GCA x environment and SCA x environment interaction effects were also significant for all traits. Inbred CML258 had the highest GCA for grain yield under drought stressed conditions and across locations. Inbred lines CML254 and CML339 had the best GCA for ears per plant across drought stress and across locations respectively. SCA effect for grain yield was highest for cross CML78 x SPLC-F (0.89 t/ha) while the best hybrid was CML258 x CML343 (4.03 t/ha) across locations. A biplot of AMMI analysis revealed that well-watered and drought stressed environments discriminated genotypes differently. Mid parent heterosis for GY was highest in the drought stress environments followed by low N stress environments.