Polyester yarn having portions which differ in dye uptake, arranged along its length in a predetermined pattern, is produced by treating portions of a spin-oriented yarn with a fluid to induce crystallization and then drawing the yarn to provide a product having a break elongation appropriate for the intended use. The spin-oriented yarn is preferably prepared by melt-spinning polyethylene terephthalate into yarn while withdrawing the yarn from the spinneret at a take-off speed of 3000 to 4000 yards per minute. Suitable treating fluids include acetone or methylene chloride at room temperature and water or air at elevated temperatures. The treated yarn can be draw-textured on false-twist texturing machines having heaters at temperatures above 200.degree. C. The treated portions of the yarn dye deeper than the untreated portions to provide attractive effects in dyed fabrics.