The vast majority of maize breeding efforts have been conducted under high N environments that primarily select for only one component of NUE, N uptake. Furthermore, these studies have employed U.S. and European genotypes, which have been selected for performance at high N. Historically, maize was grown in numerous low N tropical environments, suggesting that evaluation of adapted maize lines containing tropical germplasm may harbor useful genetic variation and novel alleles for improving NUE. The goal of this research was, first, to perform an initial evaluation of NUE and its components in a set of adapted U.S. lines with introgressed exotic germplasm and, second, to assess the genetic differences in NUE among the corresponding hybrids, in an attempt to predict the behavior of these hybrids by comparison with the inbreds. Inbreds and hybrids were grown in the field under a range of N supply (from deficient to sufficient), and nitrogen use efficiency and its components measured at maturity. There was no significant effect of N rate on NUE for the inbreds, but we were able to detect significant effects of both the N supply and the different genotypes on NUE for the hybrids. Compared to the inbred parents (B73 and Mo17) introgressing of exotic germplasm nearly always improved NUE (and both of its components) in both the inbreds and the corresponding hybrids