The objective of this study was to investigate the association of the oxygen tension in the periodontal pockets with clinical parameters of gingival inflammation of the maxillary anterior teeth of 32 patients. The pocket oxygen tension (pO2) was measured by a polarographic method with electronic compensation for temperature change. The oxygen saturation of hemoglobin (So2) in the gingiva was determined with tissue reflectance spectrophotometry. Gingival crevicular fluid flow (GCF) was measured with electronic impedance. No significant association was found between pocket pO2 and the modified gingival index, the plaque index, and GCF. Pocket pO2 showed significant correlation with probing depth (r = -0.57, P = 0.0005). Significant correlation was observed between pocket pO2 and gingival So2 (r = 0.69, P < 0.0001). When all variables were entered into a multiple regression model, only gingival So2 had a significant independent effect on the pocket pO2 (P = 0.0005). These results indicate that the oxygen sufficiency in the gingiva has a significant independent influence on the pocket oxygen tension. These studies provide the basis for understanding the oxygen tension in the periodontal pocket, which likely is a major determinant of the subgingival microflora. The studies may also lead to the development of methods for diagnosing and monitoring periodontal diseases. J Periodontol 1998;69:1127-1130.