Two maize (Zea mays) populations, Kitale Synthetic II and Ecuador 573, have undergone eight cycles of reciprocal recurrent selection at 10% selection intensity with grain yield as the major selection criterion. A study was conducted in the years 1983, 1984 and 1986 at several environments in western Kenya to evaluate direct and indirect responses to selection in the two populations and their variety cross. Neither of the populations responded to selection for yield, but their variety cross was improved at a rate of 3.6% per cycle. Percentage mid-parent heterosis for yield showed a significant linear increase (b = 3.804), presenting opportunity for further exploitation of hybrid vigour. As a correlated response to selection, percentage prolificacy increased in both populations and in their variety cross, the greatest response being observed in Ecuador 573. Ear height was reduced in Ecuador 573 but did not change in Kitale Synthetic II or the variety cross whereas maturity length was reduced in the variety cross, but did not change in either parent.