Although the knot security of suture materials has been widely investigated, there are few reports on the effects of knot tying conditions. With respect to foreign body reaction, it is preferable to use the minimum possible amount of suture materials and to use an appropriate material to ensure knot security. In this study, the different effects of knot tying conditions, such as knot type, tying force, and tying speed, were investigated. Knot tying was performed by a tensile tester for reproducible testing with the least amount of hand tying variation. The square knot (1 = 1 = 1) was shown to be the most appropriate knot type to evaluate monofilament sutures with a tensile tester. Increasing the tying speed and tying force enhanced knot security. The mechanical tying method was found to be a useful alternative to hand tying and provided reproducible test results. (C) 2008 Wiley Periodicals, Inc.