The influence of experimental neutropenia on the wound healing process in standardized excisional palatal wounds was studied in 16 guinea pigs. Corresponding wounds in 15 normal animals were used as controls. Neutropenia was induced and maintained by daily injections of heterologous anti-neutrophil serum. One-micron sections from biopsies of palatal mucosa sampled 6, 24, 48 and 120 h after wounding were evaluated with special reference to the progress of epithelial wound repair and to the occurrence and location of inflammatory cells and bacteria. In animals treated with anti-serum, neutrophilic leukocytes disappeared from the wound cavity, whereas other inflammatory cells remained unchanged. Further bacterial invasion deep into the cavity was observed. The epithelial repair took place at a deeper level in the wounds of neutropenic animals compared with those of normal animals. The rate of re-epithelialization was the same in neutropenic and control wounds. The experiment indicates that the neutrophils in oral wounds provide a principal agency for host defense against microorganisms and probably thereby indirectly determine the direction and level of epithelial cell migration.