The invention relates to diaminopyrazole derivatives having the following structure (I), wherein R.sub.1 represents an alkyl or alkenyl radical bearing at least one substituent selected from among OR, NRR', SR, SOR, SO.sub.2R, COOR, CONRR', PO(OH).sub.2, SO.sub.3X, NHCONRR, a non-cationic heterocycle, an aryl, a halogen. R.sub.2 and R.sub.3 are different from H and represent, independently of each other, an alkyl or alkenyl group; R.sub.2 and R.sub.3, together with the nitrogen atom to which they are attached, can form a heterocycle possibly comprising at least one other heteroatom selected from among N, O and S; R.sub.2 and R.sub.3 or the heterocycle that they form with the nitrogen to which they are attached can be substituted by at least one substituent defined above. The identical or different R, R' groups are selected from a hydrogen atom, an alkyl or alkenyl group; R and R', together with the nitrogen atom to which they are attached, can form a heterocycle having at least 4 ring members that can contain at least one additional heteroatom selected from among O, N and S. X represents a hydrogen, an alkaline-earth or alkali metal atom or an ammonium group. The invention also relates to the dyeing compositions and the dyeing methods using same ##STR00001##