Abstract: A marking yarn for selective use in formation of a textile fabric, such as a tubular pantyhose blank, comprises an elongate strand-like yarn base formed of a water-soluble material and at least partially coated with a material which is detectible by an ultraviolet sensor. When the marking yarn is included in the textile fabric, e.g., by knitting one or more courses of the marking yarn in plated relation with the body yarn of the hosiery blank, the yarn effectively designates a predetermined location in the fabric of the hosiery blank which can be subsequently detected by an ultraviolet sensor in the sewing of the hosiery blank into a pantyhose garment. In subsequent wet processing of the garment, e.g., dyeing, the marking yarn dissolves, thereby removing it from the fabric and liberating the coating material.