Various square knots, sliding knots, and surgeon's knots in mono- and multifilament suture material of different diameters were tested with respect to knot strength and knot security. Loop holding capacity of knots varied from 37.2 to 149.8 N, depending on the kind of knot, knot configuration, kind of suture, suture structure, and suture dimension. On the whole, square knots proved to be more reliable than sliding knots. Knot performance of surgeon's knots was not better than that of square knots. Knot security of three-throw sliding knots and two-throw square knots and surgeon's knots was rather poor. These knots cannot be recommended for clinical use. In smaller diameter mono- and multifilament suture material, knot performance of sliding knots that contained one extra throw was identical to that of square knots. It is concluded that the outcome of the comparison of square knots and sliding knots depends on knot configuration, suture material, and suture size. The implications of these laboratory findings for clinical use are discussed.