The effects of various adenosine phosphate compounds, theophylline, histamine,a nd metiamide, on steady rates of acid secretion by isolated fundic mucosa of the rabbit were measured by the pH stat method. Cyclic adenosine 3':5'-monophosphate (cyclic AMP), N(6), O(2')-dibutyryl adenosine 3':5'-monophosphate and theophylline increased the rate of acid secretion. Addition of theophylline in a concentration which has no stimulatory effect, reduces the effective concentrations cyclic AMP or histamine required for stimulation of acid secretion. Measurements of lactate, pyruvate, and CO2 appearances indicated that the increases in acid secretory rates were predominantly due to H+ and not organic acid accumulation in the luminal bath-secretion. Metiamide prevented the stimulatory effects of histamine and ATP. However, metiamide did not prevent the stimulatory effects of N(6),9(2')-dibutyryl adenosine 3':5'-monophosphate, theophylline, or 5'-AMP. The results provide further evidence for a role of cyclic AMP in governing the rate of acid secretion by rabbit stomach. The data also are consistent with histamine and ATP (at least in the concentration used) requiring adenylate cyclase activity for stimulation of acid secretion and 5'-AMP inhibiting phosphodiesterase activity.