The sensitive crystallization of copper chloride (Pfeiffer's method) is applied to aqueous extracts from leaves, stems, roots and flowers from two varieties, toxic and non toxic,, of cassava (Manihot escidenta Crantz). The comparative description of the 20 series studied shows that, even though the crystallization patterns are morphologically poor, the method has enough sensibility to be used in cassava problems. The application of sensitive crystallization: in differentiation of varieties is recomended.