The effect of the increasing degree of human gingival inflammation on adenylate cyclase (basal, fluoride stimulated) and low Km and high Km cAMP phosphodiesterase activities were evaluated in separate studies. Human gingival biopsies were classified by the Löe Bleeding Index as mildly, moderately, and markedly inflamed. Basal and F- stimulated adenylate cyclase (cAMP synthesis) activities were found to be unaltered by the increasing degree of inflammation when the data were expressed on either a mg wet wt, or mg protein basis. A significant loss of F- stimulated adenylate cyclase (mg protein) activity was observed in the moderately inflamed group when the data were compared with either the mildly or markedly inflamed groups of tissue. The low Km, and high Km cAMP phosphodiesterase activities (cAMP degradation) were found to be unaffected by gingival inflammation. This suggests that neither cAMP synthesis, nor degradation are stimulated in human gingiva by inflammation.