Three late-maturing varieties of maize (Zea mays L.) released from 1972 to 1988 and one local cultivar were evaluated in replicated field trials at Nyankpala and Damongo in 1992 and 1993. Plant densities (30 000, 50 000, 70 000 plants ha-1) were assigned to the main-plots and 12 combinations of N fertilizer levels (0, 80, 160 kg N ha-1) and varieties (Local, Composite 4, Dobidi, Okomasa) were assigned to the sub-plots in four replicates. The objective was to determine the rate of increase in grain yield due to genetic improvement under the different levels of soil fertility and plant densities. Across location analysis for grain yield showed significant (P