The effects of injecting nerve growth factor (NGF) into subdermal air sacs on the backs of mice was studied. Sequential infiltration of cells into the lining of the sacs was observed. The initial cell type to infiltrate was the polymorphonuclear leukocyte, followed by highly vacuolated mononuclear cells, and then by fibroblast-like cells. This resembles the classical pattern of cellular responses during the normal process of wound healing. The kinetics for the peak accumulation of each cell type were dependent upon the concentration of NGF injected, and significant acceleration of infiltration of each cell type was observed with as little as 1 nM NGF. A similar acceleration of cellular infiltration was observed when mice were injected with the synthetic chemotactic peptide n-formyl-methionyl-leucyl-phenylalanine. This finding suggests that application of any chemotactic factor to wound sites may lead to accelerated tissue repair and an enhanced rate of wound contraction. The observation that NGF can act as a chemotactic factor in vivo may explain its ability to accelerate the healing of experimentally induced wounds in mice.