The purpose of this investigation was to determine the security of the square knot tied with one looped end and one free end versus the security of the square knot tied with two free ends. Size 4/0 and size 6/0 monofilament nylon, polypropylene, and Biosyn sutures were selected for this evaluation. The mechanical performance of these sutures was judged according to knot breakage force and number of throws required to attain security. Knots with one looped end and one free end require more throws to ensure knot security than do knots constructed from two single suture strands of comparable sizes and types of sutures.