Based on the literature dysfunction of splanchnic circulation may be assumeol in the development of severe acute pancreatitis. Abnormal gut functions investigated by routinely used clinical examination is not available. Gastric tonometry indirectly gives information about gut function. Authors followed prospectively 12 patients who suffered from acute pancreatitis. Four patients recovered without complications, 4 patients had different complications and 4 patients died. Gastric intramucosal pH (pHi) was measured by TRIP NGS catheter and Tonocap monitor. Measurements were started at the time of hospitalisation and repeated every six hours on the first 3 days. Intramucosal acidosis (pHi < 7.3) could be measured independently from aetiology. Gastric pHi showed strong correlation with Acute Physiology and Chronic Health Evaluation II. (APACHE II) score (p = 0.02). APACHE II scores were significantly higher in-group pHi < 7.2 (13.9 +/- 1.7) compared to group pHi > 7.2 (7.33 +/- 1.06) (p = 0.002). 24-hour changes in APACHE II scores were significantly greater in the cases of pHi < 7.2 (3.3 +/- 1.47) versus pHi > 7.2 (-0.6 +/- 0.97) (p = 0.03). Changes of pHi in the early phase of acute pancreatitis indicate that splanchnic circulation is already involved and the pHi may have a prognostic value.