Gingival fluid from eight control subjects and ten diabetics was collected and the content of cAMP and protein in the fluid was assayed to determine the nature of the biochemical changes occurring in the gingival fluid due to diabetes. The gingival fluid of the control subjects had a cAMP concentration of 2.4 X 10(-6) M, which was a hundredfold greater than that seen in serum, thus suggesting that the cAMP in the fluid resulted from active synthesis by the gingival cells and was not merely a transudate from the blood. The gingival fluid of the diabetics contained only one-seventh the level of cAMP seen in the control group. It is suggested that the decreased level of cAMP seen in the givgival fluid of diabetics may be a manifestation of a defect in the cAMP forming mechanism of the gingival tissue, which may reflect the systemic etiology of diabetes. It was also found that in the control subjects the content of cAMP in the gingival fluid was in inverse proportion to the volume of exudate in the gingival crevice. No such relationship was seen in the diabetic group. It appears that the level of cAMP present in the gingival fluid of normal individuals without any generalized endocrine deficiencies may be used as an additional indicator of the inflammatory status of the gingival tissues, along with the clinical evaluation based on gingival index.