A process is described for the preparation of pure, asymmetric 1:2 chromium complex dyes containing at least two groups which impart solubility in water, which process comprises reacting a mixture of two dyes of the formulaeF.sub.1 --(SO.sub.3 H).sub.t (1)andF.sub.2 --SO.sub.2 --Y (2)in which the symbols are as defined in claim 1 with a chromium donor in a molar ratio of 0.85:1.0 to 1.2:1.0 in a one-pot process under pressure at a temperature above 100.degree. C. and at a pH between 0 and 2 and then continuing the reaction at a slightly acid, neutral or slightly alkaline pH. The dyes obtained by the process according to the invention are suitable for dyeing, in particular, wool, silk, leather and synthetic polyamide fibres.