57th Communication on Investigations in Textile Chemistry, for 56th Communication see ref. J.Silk was dyed with twelve reactive dyes containing various reactive groups. The dyeings were thoroughly extracted so that all non‐covalently bonded dye was removed. The extracted dyeings were treated with buffer solutions in the pH range 1.89 to 10.65 at 70°C for 24 h. The exhaustion, fixation ratio and extent of reaction of the dyeings and the rate of hydrolysis of all dyed samples in six buffers were measured. The dye‐fibre bond was found to be sufficiently resistant to hydrolysis for ail dyeings. The fixation ratio and wet fastness were particularly good for dyeings with α‐bromoacrylamide groups and with difluorochloropyrimidine