An improved method for increasing the relative viscosity and molecular weight of a polyamide polymer (such as nylon 6,6, nylon 6, and the like) while in the solid state involving the use of a phosphorus-containing catalyst (such as 2(2'-pyridyl) ethyl phosphonic acid or the like) in combination with an oxygen free gas characterized by a low dew point (typically below 30.degree. C. and preferably below -30.degree. C.). The combination of affording commercial operation at greater through put at lower temperature. Such a process is of particular value during the production of terpolyamide and multipolyamide polymer intended for use in colored nylon fiber manufacture.