The phenomenon of wound contraction has been studied in the skin of rats, rabbits and guinea pigs with the aim of obtaining a standardized wound system to be used for biological assay of in vivo agonists and antagonists of granulation tissue contraction. The sex of the animal, the time of day of wounding, the size and the shape of the wounds all had no apparent influence on the wound contraction curves expressed as per cent of original area against time. The test animal's age and species did have a significant influence on contraction of skin wounds which by analogy with results obtained with rigid splints attached to the skin could be attributed to variations in the thickness, rigidity and fixation of the skin to deep tissues. The shape of the final scar was influenced by the position of the wound on the body surface. The major factor in this instance was considered to be tensile forces acting within the skin. Wound contraction curves in rats and rabbits showed three distinct phases, namely early closure, stationary and logarithmic closure. Guinea pigs lacked the early closure phase. The exact role of the panniculus carnosus in wound healing is considered to be worthy of detailed study.