Four wheat cultivars showing different reactions to Al toxicity under field conditions and presenting a great variation in plant height were screened in nutrient solution with different concentrations of aluminum. The tall Brazilian cultivar, 'BH-1146' was tolerant to 10 ppm of Al; 'Atlas-66' developed in North Carolina was tolerant to 6 ppm but moderately tolerant to 10 ppm of aluminum. The dwarf cultivar Tordo, a Tom Thumb source of dwarfism, was tolerant to 2 ppm but totally sensitive at 6 ppm. The Mexican semidwarf cultivar Siete Cerros, a Niorin-10 derivative, was sensitive to 2 ppm of Al. Parents, F1 and F2 generations from the crosses between tolerant ('BH-1146' and 'Atlas-66') and sensitive ('Tordo' and 'Siete Cerros') cultivars to 6 ppm were screened under 3 ppm and the same genotypes plus the backcrosses to both types of parents (BCª and BCb) were screened at 6 ppm. Parents, F1 and F2 progenies from BCª and BCb involving the cross BH-1146/Siete Cerros were retested under 3 and 6 ppm of Al. Parents, F1 and F2 for the cross between 'BH-1146' and 'Atlas-66' were screened under 6 and 10 ppm of Al. At 2 and 3 ppm of Al, parents, F1 and F2 from the cross Tordo/Siete Cerros were studied. The results obtained suggest that 'BH-1146' differs from Atlas-66, Siete Cerros and Tordo by one pair of dominant gene. This pair of gene was efficient even at 10 ppm of aluminum, so should be used in a breeding program towards aluminum tolerance when high levels of this element are involved. The cultivar Atlas-66 showed to have two pairs of dominant genes for Al tolerance but when the aluminum concentration increased from 3 and 6 to 10 ppm these pairs of genes became less efficient. 'Tordo' differs from 'Siete Cerros' by a pair of dominant gene for tolerance at 2 ppm of Al. So 'Tordo' would be useful as a source of tolerance when low levels of aluminum are involved. There was a gradual decrease of dominance of the pair or pairs of genes, or of the complex of genes which could be transmitted as a block, responsable for the tolerance reaction as the aluminum concentration in the nutrient solution increased for all hybrid populations under study.