This study was undertakento determine whether there is any correlation of temperature within periodontal pockets with their depths. Pocket temperatures were measured with a thermocouple at 1 mm intervals of depth in 247 pockets, in 20 patients with periodontitis, mesiobucally and mesiopalatally/mesiolingually in relation to 6 standard teeth. Pocket temperatures increased consistently with pocket depth. Maxillary pockets were cooler than mandibular pockets, but in both jaws the differences between buccal and palatal/lingual pockets were not statistically significant. The findings are in keeping with knowledge about the increased temperature of inflamed tissues and the study appears to have relevance to the diagnosis of disease activity in pockets, but further studies are necessary to establish reference levels of pocket temperature.J Periodontol 1991;62:95– 99.