Experiments were conducted to investigate the ultraviolet irradiation of wool fabric as a pretreatment for differential dyeing. Wool fabric was irradiated using a medium-pressure mercury lamp in order to obtain, on the irradiated area, increased dye uptake under the same dyeing conditions as untreated wool. The chemical modification of the fibre surface as a result of ultraviolet irradiation was confirmed by an increase in metal ion absorption and hydrophilicity, in agreement with Fourier Transform-infrared–attenuated total reflectance spectra, although scanning electron microscopy showed that the fibre morphology was unaffected. A selection of 1:1 metal-complex dyes was used to show the maximum colour difference between irradiated and untreated areas of the fabric. The experiments focused on two effects: a double face with the same shade but different depths (greater depth on the treated side), and a double face with different shades. The latter effect was achieved by dyeing the irradiated fabrics with mixtures of acid and metal-complex dyes. Rubbing and washing fastness evaluations at 50 °C confirmed that the dyeings after irradiation with the selected 1:1 metal-complex dyes scored identically to conventional dyeings.