The effects of gastrin, histamine and PGE1 on adenylate cyclase (AC) activity of gastric mucosal cells from the canine stomach were investigated.In the cell membrane fraction, which was purified from a 800-100,000xg pellet of homogenate by a continuous linear gradient with sucrose, AC and Mg2+-ATP ase activity was shown to be 3.9 and 4.1 times as large as that of the homogenate, respectively. Dispersed cells were obtained by digesting gastric corporal mucosa with 0.075% collagenase, and parietal cell-rich fraction and non-parietal cell fraction were obtained by fractionating with the gradient sedimentation method in the nonlinear gradient of Ficoll. Cell viabilities of dispersed cells, parietal cell-rich fraction and non-parietal cell fraction were 88, 65 and 64%, respectively. Percents of parietal cells in those fractions were 12, 44 and 5%, respectively. Ac activity was determined by measuring the amount of cAMP produced. Cyclic AMP produced was measured by RIA. One to 3 X 10-5M pentagastrin and/or 5 X 10-6M synthetic human gastrin 1, 10-3M histamine and 10-4M PGE1 were employed as stimulators of AC activity.Basal AC activity of the homogenate, cell membrane, dispersed cells, parietal cell-rich fraction and nonparietal cell fraction were 5.9 pmol cAMP/mg·min, 22.9 pmol cAMP/ mg· min, 3.6 pmol cAMP/106 viable cells·15min, 3.3 pmol cAMP/106 viable cells·15min and 2.7 pmol cAMP/106 viable cells?15min, respectively.In all preparations, no stimulations of AC activity by gastrin were detected. On the other hand, histamine activated AC significantly in cell membranes, dipersed cells and parietal cell-rich fraction. Percent stimulation of AC activity by histamine in these preparations were 158,179 and 154%, respectively. However, histamine failed to activate AC significantly in homogenate and non-perietal cell fraction. PGE1 also activated AC significantly in all preparations and percent stimulations of AC activity by PGE1 in homogenate, cell membrane, dispersed cells, parietal cell-rich fraction and non-parietal cell fraction were 204,158,300,244 and 455%, respectively. The stimulation of AC activity by PGE1 in non-parietal cell fraction was much greater than that in parietal cell-rich fraction.The above data indicates that histamine stimulated AC activity of parietal cells, and PGE1 stimulated AC activity of non-parietal cells. In addition, it was suggested that the intracellular mechanism of the action of gastrin in gastrin corporal mucosa was independent of the AC-cAMP system because no effect of gastrin on AC activity was detected. Therefore, another intracellular mechanism by which the effect of gastrin is mediated will have to be elucidated in gastric corporal mucosa.