Tissue response to injury caused by the electrosurgical scalpel, the hemostatic Shaw scalpel, the CO2 laser, and a standard steel scalpel have been compared. Subcutaneous incisions in pigs were evaluated histologically at 1, 4, 7, 14, and 22 days postincision. The least damage was produced by the standard steel scalpel at all time periods. Epithelial migration started on day 1 for the standard steel scalpel, on day 4 for the Shaw scalpel, and only on day 7 for the electrosurgical scalpel and laser knives. Lateral thermal necrotic zones were found for all three thermal knives. Tensile testing showed no significant differences in the early postincision tissue strength. By day 14 wounds made with the standard steel scalpel were stronger than those made with the Shaw and electrosurgical scalpel. These findings indicate that thermal injury delays the wound healing process.