Abstract: This paper describes the changes in protein content, nucleic acids (RNA and DNA) content as well as the activity of glucose-6-phosphate dehydrogenase (G6PDH) and glyceraldehyde-3-phosphate dehydrogenase (G3PDH) in seedling (5-d-old) of sensitive-cultivar contender and in tolerant-cultivar Giza 3 treated with increasing concentrations of aluminium. Rapid increase in G6PDH (EC 1.1.1.49) and G3PDH (EC 1.1.1.40) activities were observed in Al-resistant cultivar, while no change in the activities of the two enzymes were observed in Al-sensitive cultivar during 5 days of germination. Rapid decreases in protein, RNA and DNA contents in sensitive-cultivar and in resistant-cultivar (at 150 M Al), were observed in seedlings treated with Al. On the other hand, significant increases in protein, RNA and DNA contents were observed in resistant cultivar treated with 50 and 100 μ M Al. These results suggest that rapid induction of G6PDH and G3PDH in the Al-resistant cultivar by Al may play a role in the mechanism of Al resistant, possibly by regulation of the pentose phosphate pathway and alteration in either lipid composition of plasma membrane (El-Saht, under publication), or alteration in nucleic acids and protein contents.