The temperature changes of the labial gingiva and mucosa of the maxillary incisor regions were investigated using computer-assisted thermography. 9 patients with destructive periodontal disease (7 female and 2 male, aged between 12 and 33 years, undergoing periodontal treatment for periods varying from 6 months to 12 years) and 10 volunteers with clinically normal periodontia (6 female and 4 male, aged between 19 and 26 years) took part in this study. The gingivae and mucosae were initially cooled using a homogeneous flow of air (15 l/min at 15 degrees C) for 3 min. 20 s after the cooling phase, temperature increases of these soft tissues were sequentially recorded using 48 thermograms per person. This procedure was repeated 4 times for each person examined. The weighted mean of the time constants of the tissue re-warming curves was significantly higher (p less than 0.025) for the periodontitis group (152 +/- 6 s) compared to the clinically healthy group (110 +/- 9 s). The different thermodynamic behaviour between the 2 groups studied indicated differences in the blood-flow and/or its regulation.