Tissue strength to breaking point against the pulling forces of a suture was investigated in the musculo-aponeurotic layer of the six laparotomy incisions most commonly used in surgery, namely 1) mid-line incision, 2) paramedial incision, 3) pararectal incision, 4) transverse incision, 5) right oblique subcostal incision, and 6) McBurney's incision. When the suture length was 5 mm and the interval between sutures 10 mm, the mean tissue holding power was 1.9 kp for peritoneum and transversalis fascia together; 5.6 and 3.2 kp for longitudinal incisions through andinary sutures; and 22.9 kp for linea alba with sutures placed lateral to the transition between linea alba and rectus sheath. In comparison with these longitudinal incisions the tissue-holding power in corresponding tissues in transverse incisions was greater (c. 40% greater in the linea alba and anterior rectus sheath and c. 60% greater in the posterior rectus sheath). When regard was paid to the total closure strength of the musculo-aponeurotic layer, e.g. in paramedian incisions the sum of the figures for the anterior and posterior rectal sheaths, the paramedian incision was found to give the weakest closure, followed by the only slightly stronger pararectal incision. The strongest closure was obtained with the midline incision through the linea alba when the sutures were placed laterally to the transition between the linea alba and the rectus sheath. The values for holding power recorded for the musculo-aponeurotic layer may provide a rational basis for the choice of thread dimension and knot type in order to create a suture loop that will be at least as strong as the tissue.