OBJECTIVE: To investigate the effects of nicotine on periodontal membranes and alveolar bone using histopathological and immunohistochemical methods. STUDY DESIGN: Rats were divided into 2 groups: those systemically treated with nicotine sulfate (2 mg/ kg subcutaneously, daily) for 28 days, and untreated controls. We analyzed the distribution of osteonectin and osteopontin immunohistochemically, with antibodies, in the maxillary region. RESULTS: In the treatment group, resorption of alveolar bone and vascular dilation, bleeding, periodontal membrane degeneration, hyalinization, and necrosis were seen in some areas. Negative osteoblastic activity was observed in immunohistochemical analyses of collagen fibers in the periodontal membrane. CONCLUSION: In short- and long-term nicotine consumption, soft tissue and alveolar bone are negatively affected during cell proliferation. This phenomenon may lead to a delay in treatment of implantation. © Science Printers and Publishers, Inc.