The polychromy of the monumental portals of the Gothic Cathedral of Bourges was studied. Sample cross-sections, microchemical analyses, and staining tests were carried out, supplemented by thin-layer chromatography and x-ray fluorescence analysis. The polychromy of the south lateral portal, first painted in 1225 and repainted after about 30 years (as determined from the analytical results and historical information) shows some differences with respect to the polychromy of all the other portals (five in the west façade, one lateral facing north). Differences in the range of pigments and the medium used (oil in the south portal, casein in the others) as well as other variations in the technique were observed. The polychromy of Gothic stone sculptures is discussed with regard to the painting technique on the basis of the present results, compared with those which have emerged from the examination of other sculptural monuments.