In several Brazilian acid soils, the extractable aluminum with the solution of 1.0 mol L-1 KCl (Al-KCl) may exceed 10 cmol c kg-1 , but in some soils the presence of this element seems to exert little or no interference in the productivity of the plants. The study aimed to evaluate in which conditions the high levels of Al-KCl are related to the toxicity in soybean and maize plants cultivated in greenhouse, and their possible interference in the dry matter production of the same. Also, it aimed at assessing the soil chemical attributes that best identified a probable Al toxicity and the responses of the cultivated plants to liming. Al-KCl is not related to the manifestation of toxicity by the plants, nor did it interfere in the productivity of the plants cultivated in the AC9 and RS soils. On the other hand, the high levels of Al-KCl interfered in the productivity of these plants cultivated in the PE, BR and CB soils, manly in the treatments without limestone. Aluminum saturation, sum and base saturation were the best soil chemical attributes for the identification of Al toxicity and plant response to liming.