Purpose: The aim of this in vivo study on dogs was to investigate and compare the inflammatory potential of four different retraction agents on the gingival connective tissue. Materials and Methods: All procedures on eight beagle dogs were performed under general anesthesia: taking oral hygiene measures, placing retraction cords medicated with four chemical agents into the gingival sulci, and taking tissue biopsies. The specimens were evaluated after a 10-minute exposure to chemical agents. The inflammatory response of the connective tissue underlying the sulcular and junctional epithelium triggered by retraction agents was assessed quantitatively. Microscopic images of tissue specimens were morphometrically analyzed using a computer-assisted morphometric method. Results: The most intense inflammatory response in the connective tissue underlying the sulcular epithelium was triggered by astringent retraction agents-Racestyptine in specimens taken after 1 day and 1 week and Rastringent after 1 day (P .05). Tetrahydrozoline-sympathomimetic vasoconstrictor (Visine) was found to have the lowest inflammatory potential. Retraction chemicals produced no significant effects on the connective tissue subjacent to the junctional epithelium. The ratio of the connective tissue area to that of the inflammatory infiltrate showed that 25% aluminum chloride (Racestyptine) was the most aggressive and tetrahydrozoline the least aggressive retraction agent used. Conclusion: All the retraction chemicals tested increased the infiltration with inflammatory cells in gingival connective tissue.