Two experiments with different genotypes of barley (Hordeum vulgare L.) and oats (Avena sativa L.) growing in nutrient solution were carried out for testing acidification capacity of each cultivar. and their different tolerance to acidíty (W) and aluminium (Al). Both experiments were peñormed with the addition of N-NH4+ N-NO3- and NH4NO3 as N source. Two barley (Andes 3.84 (F) and Frontera) and two oats genotypes (Llaofén-INIA and Nehuén-INIA) were used for testing acidification capacity and were grown in nutrient solution measured for pH at 14 and 18 days. For screening plant tolerance to H+ and Al, four barley (Andes 3.84 (F), Andes 59.82, Andes 96.82 and Frontera) and the two oats genotypes from above were used. Plants were grown in nutrient solutions at pH 4.0, 4.5, 5.0 and 6.0 with the addition of 0, 25, 50 and 100 μM Al to barley seedlings and 0, 50, 100 and 200 μM Al to oats seedlings, respectively. Length and weight of root and aerial part were measured. Results showed that N-NH4+ addition produced H+ root excretion in both cultivars being higher in oats. As to N-NO3- it produced OH- extrusion which was also higher in oats cultivars. In relation to tolerance, oats were found more tolerant to H+ and Al than barley. Available data allow the following rankings for barley: a) For H+ sensitivity: Andes 96.82 > Andes 3.84 (F) > Andes 59.82 > Frontera; and b) For Al tolerance: Frontera> Andes 3.84 (F) > Andes 59.82 > Andes 96.82.