Abstract: Uniformity of properties of spun polyamide filaments is improved by treating flake polyamide with successive nitrogen gas streams, the first having a variable temperature and water content, and the second being dry but having a variable flow rate. Viscosity of the molten polyamide from a melter for the flake is determined by measuring differential pressure across a transfer pipe. The viscosity measurement is used by automatic control apparatus to control the flow rate of the second stream, and the moisture content of a make-up stream added to the first stream. The flow rate of the make-up stream is controlled to maintain the second stream within limits, and the temperature of the first stream is controlled to maintain the flow rates of the make-up and second streams within limits.