The invention comprises mono- and poly-azo dyes of the formula: <FORM:0858562/IV (c)/1> (where R is the radical of a diazotizable or tetrazotisable aromatic amine containing benzene or naphthalene rings, and X, which is in ortho position to the azo bridge, is hydrogen or a metallizable group, or a group convertible to a metallizable group during metallisation, R1 is a phenyl group or a substituted phenyl group, and n is 1 or 2) and their metal complexes with metals of atomic number 24-30 e.g. Cr or Co. The dyes may be made by coupling one mole of a diazonium or tetrazonium compound derived from an aromatic amine containing in ortho position to the amino group or groups an appropriate group X, with 1 or 2 mols of 1-phenyl -3- methylpyrazolone -(4) or its phenyl substituted derivatives, e.g. derivatives in which the phenyl group is substituted by halogen, alkyl, hydroxyalkyl, nitro, amino, carboxy, sulphonic acid, sulphonic acid amide, alkyl sulphone, or aryl sulphone groups. Examples of suitable diazo components are aniline, and 1- and 2- aminonaphthalene which may be substituted by halogen, alkyl, aryl, hydroxyalkyl, hydroxy, nitro, carboxylic acid, sulphonic acid, carboxylic amide, amino, or acylamino groups. Tetra-azotisable diamines such as 4. 41-diaminodiphenyl and its derivatives containing bridge members between the two phenyl groups e.g. -CH2-, -CO-, -NH-CO-NH, -S-, and -SO2-, and di- and tetraazotisable mono- and polyazo dyestuffs may also be used as diazo components. The reaction of the pyrazolones with the diazo compounds may be carried out in alkaline media or in presence of acid-binding or acid-neutralizing agents. When the dyes contain hydroxyl, alkoxy, amino, or carboxyl groups in adjacent position ot the azo bridge, they may be converted into their metal complexes. Metal complexes containing one atom of metal for each molecule of dyestuff may be reacted with other metallizable monoazo or azomethine dyes or with colourless complexforming compounds, and mixed complexes may be formed by metallizing the corresponding dyestuff mixtures under conditions such that there is more than one molecule of dyestuff for each atom of metal. The dyestuffs may be used as pigments or as dispersion dyes, and may be used for dyeing wool, silk, leather, polyamides, natural or regenerated cellulose fibres, cellulose ester varnishes and lacquers. Brown, blue, and black dyeings may be obtained. Examples are given of the preparation of monoazo dyes from (1) 1- amino -4- chlorobenzene, (2) 1- aminonaphthalene -2- sulphonic acid, (3) 1- amino -2-methybenzene -5- sulphonic acid, (4) 1- amino -4-methybenzene -3- sulphonic acid, (5) 1- amino -4-nitro-benzene -2- sulphonic acid, using 1- phenyl-3- methylpyrazolone (4) as the coupling component. The preparation of other dyestuffs of the stated general formula is given. Diazo components specified include 1- aminobenzene -4-sulphonic acid, 1- amino -8- hydroxynaphthalene -3. 6- disulphonic acid, 1- aminobenzene -2-sulphonic acid- (N- benzyl)- amide. The coupling component may be 1- (41- sulpho)- phenyl -3-methylpyrazolone- (4). The compound 4. 41-diaminodiphenyl sulphide is diazotised and coupled with 1- amino -8- hydroxynaphthalene-4, 6- disulphonic acid; a diazo solution prepared from 1- amino -4- nitrobenzene is added and then further coupling is effected with 1-phenyl -3-methylpyrazolone- (4) to form a product which dyes leather a dark blue shade. The compound 4. 41- diaminostilbene -2. 21- disulphonic acid is diazotised and coupled with 1-phenyl -3-methylpyrazolone- (4). The dyestuff prepared from 1- amino -2. 5- dimethoxybenzene -4-sulphonic acid amide and 1- phenyl -3- methyl-pyrazolone- (4) is reacted with chromium chloride in ethylene glycol to form a complex which may be reacted with 2- hydroxybenzoic acid -5- sulphonic acid phenylamide or with an azomethine dye, obtained from 2- hydroxybenzaldehyde and 1- hydroxy -2- aminobenzene-4- sulphonic acid amide in formamide, to obtain dyes suitable for dyeing wool. Specifications 692,073 and 785,185 are referred to.