Thermosol dyeing is a continuous dyeing process for synthetic fibers and their blends. Various auxiliaries are used in thermosol dyeing, including buffers, antimigrants and wetting agents. Non-ionic surfactants are generally used as wetting agents. It has been reported that some non-ionic surfactants cause a significant change in dye uptake in the thermosol process, the nature of which is the subject of some debate. In this study the nature of the influence that non-ionic surfactants exert on dye fixation in the thermosol process is studied. It was shown that non-ionic surfactants may act as fixation accelerants in the thermosol process, accelerating the rate of dye dissolution in auxiliary melt, thereby increasing the overall rate of thermo-fixation dyeing. At high surfactant concentrations, dye retention in surfactant may result in surfactants exerting an adverse influence on dye fixation. Dye decomposition in surfactant may also play a significant role in determining the nature of