Diazo dyestuffs containing at least one sulphonic acid group and of the general formula R1-N=N-R2-NH-OC-R3-N=N-Py, (wherein R1 represents the residue of a hydroxybenzene-o-carboxylic acid, R2 a benzene or naphthalene residue to which the azo linkage and the -NH- group are attached otherwise than in o-position to one another, R3 a benzene residue to which the -OC- group and the azo linkage are attached otherwise than in o-position to one another, and Py the residue of a 5-pyrazolone free from amino groups which is bound to the azo linkage in the 4-position and contains a hydrocarbon radical as a substituent in the 3-position) are manufactured by coupling a diazo compound of a monoazo dyestuff R1-N=N-R2-NH-OC-R3-NH2 with a 5-pyrazolone free from amino groups and containing a hydrocarbon radical in the 3-position, or by coupling a diazo compound of a monoazo dyestuff H2N-R2-NH-OC-R3-N=N-Py with a hydroxybenzene-o-carboxylic acid, the components in either case being so selected that at least one sulphonic acid group is present in the product. The starting materials R1-N=N-R2-NH-OC-R3-NH2 may be prepared by (i) condensation of a nitro-benzene-m- or p-carboxylic acid halide (e.g. m- or p-nitrobenzoyl chloride), followed by reduction (e.g. by means of alkali sulphide), with an aminoazo dyestuff R1-N=N-R2-NH2, which in turn is obtainable by (a) coupling a diazotized aminophenol-o-carboxylic acid (e.g. 4-aminophenol-2-carboxylic acid or its 6-chloro-, 6-methyl or 6-sulpho derivative, or 6-amino-phenol-2-carboxylic acid 4-sulphonic acid) with a p-coupling amine of the benzene or naphthalene series (e.g. 1-amino-2-methoxy- or ethoxy-5-methylbenzene, m-toluidine, m-anisidine, 1-amino-2 : 5-dimethoxy- or diethoxybenzene, 1-amino-2-ethoxy-5-methoxybenzene, 1-aminonaphthalene or its 6- or 7-sulphonic acid or a mixture of the last two compounds), or (b) coupling a diazotized amine of the benzene or naphthalene series containing, otherwise than in o-position to the amino group, a group, such as a nitro or acidylamino group, convertible to an amino group (e.g. m-or p-nitraniline, 4-nitraniline-2- or 3-sulphonic acid, 4-acetylaminoaniline or its 2- or 3-sulphonic acid) with a hydroxybenzene-o-carboxylic acid capable of coupling (e.g. salicylic acid or 6-methyl- or 6-chloro-phenol-2-carboxylic acid) and then reducing the nitro group or hydrolysing the acylamino group, or (c) introducing further substituents in the course of these reactions (e.g. by sulphonating 4 - nitro - 41 - hydroxy - 31 - carboxy - 1 : 11 azobenzene and then reducing the nitro group, to produce 4 - amino - 41 - hydroxy - 31 - carboxy - 1 : 11 - azobenzene - 51 - sulphonic acid, according to Swiss Specification 243,602, or by similarly treating the dyestuff m-nitraniline---> salicylic acid); or (ii) in suitable cases condensation of an amino-acylamino compound of the benzene or naphthalene series in which the amino and acylamino group are not in o-position to one another (e.g. 4-acetylaminoaniline or its 2- or 3-sulphonic acid) with a nitrobenzene m- or p-carboxylic acid halide, hydrolysis of the acylamino group, diazotization, coupling with a hydroxybenzene-o-carboxylic acid, and reduction of the nitro group. The 5-pyrazolones, free from amino groups, suitable for coupling with the diazo compounds of the foregoing intermediates, preferably carry a methyl group in the 3-position and may or may not contain in the 1-position a substituent, especially an aryl residue (e.g. of the naphthalene or preferably the benzene series) which may contain substituents (e.g. halogen atoms or alkyl, alkoxy, nitro, sulphonic acid, sulphonamide, hydroxy or carboxyl groups), examples being 3 - methyl - 5 - pyrazolone, 1 - phenyl3-methyl-5-pyrazolone and its 31-nitro, 41sulpho, 41 - hydroxy - 51 - carboxy, 51 - sulpho41 - hydroxy - 31 - carboxy and 41 - chloro - 31-carboxy derivatives, and 1-(81-sulpho-21-naphthyl)-3-methyl-5-pyrazolone. The starting materials H2N-R2-NH-OC-N=N-Py may be prepared by condensing an amino-acylamino compound of the benzene or naphthalene series, in which the amino and acylamino group are not in o-position to one another, with a nitrobenzene-m- or p-carboxylic acid halide, reducing the nitro group, diazotizing, coupling with a 5-pyrazolone of the kind defined (e.g. certain of those specified above) and then hydrolysing the acylamino group; or in some cases the corresponding diazoazo compounds are obtainable by unilateral coupling of a tetrazo compound of a diamine H2N-R2-NH-OC-NH2 with the pyrazolone. Suitable hydroxybenzene-o-carboxylic acid for coupling with these diazoazo compounds are 6-methyl- or 6-chloro-phenol-2-carboxylic acids. The products are suitable for dyeing and printing cellulosic materials (e.g. linen, cotton, and artificial silk and staple fibres of regenerated cellulose), yielding yellow to yellow-orange tints dischargeable by the neutral or alkaline discharge printing process. They may be treated in substance, in the dyebath or on the fibre with agents yielding metal (e.g. chromium, nickel, cobalt, manganese, iron or especially copper). Examples illustrate both methods of making the dyestuffs, using certain of the components specified above. In a further example, cotton sateen is dyed with the dyestuff 4-(41-aminobenzoylamino) - 41 - hydroxy - 31 - carboxy - 1 : 11-azobenzene - 51 - sulphonic acid--->1 - (31-nitrophenyl)-3-methyl-5-pyrazolone and printed with a discharge paste containing sodium formaldehyde sulphoxylate, British gum thickening, potassium carbonate, glycerine and water. Specification 455,274 is referred to. The Specification as open to inspection under Sect. 91 comprises also the manufacture of dyestuffs in which the pyrazolone residue may contain an amino group, e.g. as a substituent in an aryl group in the 1-positions. This subject-matter does not appear in the Specification as accepted.