The surface alkaline hydrolysis of fibers made from poly(trimethylene terephthalate) (PTT) was studied after extruding the polymer at high spinning speeds from 2000 to 6000 m/min and heat setting in the range of temperatures from 100 to 180degreesC. Fiber weight loss increased with an increasing heat-setting temperature but it was also dependent on the spinning speed. Some of the partially hydrolyzed fibers had a well-developed, hydrophilic surface, and pore size in the range of 0.69 to 1.20 mum. The optimum reaction and morphological conditions for increasing porosity in PTT fibers depends on spinning speed and heat-setting temperature. A temperature of 180degreesC is the upper limit for heat-setting PTT filaments but seems to be the most effective for making porous fibers. (C) 2004 Wiley Periodicals, Inc.