The results of a comparison between the effects of sodium hydroxide and calcium hydroxide on poly(ethylene terephthalate) fabrics are presented. Calcium hydroxide can produce weight-loss effects similar to an aqueous solution of sodium hydroxide. The effects of some treatment variables on weight loss, fiber diameter, bending rigidity, and strength of yarns taken from fabrics are examined. The results are explained in terms of current views of polyester alkaline hydrolysis.