The objective of the study was to determine, in the absence of competition (0·74 plants/m2), the existing variation within lines of maize (Zea mays L.) for plant and ear traits (yield per plant, number of tillers, number of ears, plant height, number of nodes, ear length, and kernel row number), as well as the relationship between hybrid potential yield per plant (i.e. yield per plant in the absence of competition) with line traits. Two categories of material were tested in honeycomb trials, grown from 1989 to 1995 in the University farm of Thessaloniki, Greece. The first category were selections from long-term inbreds B73 and Mo17, derived through honeycomb design in the absence of competition, and their crosses. Inbred selections and their crosses were evaluated in different years. For the second category two sets of S5 lines, A and B, derived through controlled selfing from the commercial single- cross hybrid PR 3183, were used in random crosses between S5 plants of lines A and B and resulted in 40 triplets; each triplet included each of the selfed parent, and their hybrid. Triplets of A and B S6 lines and A × B S5 × S5 crosses were evaluated in the same experiment. Significant differentiation among lines and hybrids was found for almost all traits; variation within lines for potential yield per plant, even in case of B73 and Mo17, seemed to be transmissible to the hybrids. Although correlation values were small in the case of B73 and Mo17 selections, there was a positive correlation between hybrids and lines for their potential yield per plant. Selection for high yield within S lines gave ‘prolific’ plants, with line prolificacy being correlated with hybrid potential yield per plant.