The wound healing process is initiated as soon as tissue is injured. Herein, we demonstrate that c-fos and c-myc mRNA transcripts are promptly increased in the wounded tissue in vivo and in vitro. A buffer solution from scraped serum-starved quiescent fibroblasts, when added to resting fibroblasts, caused the increase of c-fos and c-myc mRNA among the indicator cells. Soluble factors contained in the wounding supernatant are responsible for these phenomena and we call them wounding factors. Addition of proteinase inhibitors to the culture medium drastically reduced the c-fos mRNA induction by the wounding factors. Exogenously added trypsin or thrombin mimicked the activity of wounding factors. These results suggest that wounding causes soluble factors including various proteinases to be released from the damaged cells, which trigger the adjacent cells to respond to the injury.