Fecal pancreatic elastase 1 (PE-1) has been advocated as a noninvasive marker of pancreatic function and allows detection of moderate and severe exocrine insufficiency. Few studies have evaluated the utility of measuring PE-1 in duodenal fluid for the diagnosis of pancreatic insufficiency. Our purpose was (1) to determine the feasibility of measuring PE-1 concentrations in duodenal aspirates obtained through our endoscopic pancreatic function test (ePFT) in healthy subjects and patients with chronic pancreatitis (CP) and (2) to determine correlations between duodenal PE-1 concentrations and bicarbonate and lipase concentrations in duodenal fluid. Healthy subjects (HS) and CP patients underwent an ePFT with CCK or secretin. CP was defined as endoscopic retrograde pancreatography (ERP) Cambridge class III-IV, endoscopic ultrasound (EUS) score >5, or presence of pancreatic calcifications on CT scan. Duodenal fluid PE-1, lipase, and bicarbonate concentrations were measured in each study group. Duodenal lipase and bicarbonate concentrations were measured using an autoanalyzer (Roche Diagnostics, Indianapolis, IN). PE-1 was measured using an ELISA (Genova Diagnostics, Asheville, NC). Ten HS and 10 CP patients were studied. In the CCK test the median peak lipase for HS and CP was 1605 and 113 IU/L, respectively (P < 0.008). In the secretin test the median peak bicarbonate for HS and CP was 102 and 40 mEq/L, respectively (p < 0.008). Median PE-1 concentrations for HS and CP were 317 and 63 microg/ml, respectively, after CCK stimulation (p = 0.046) and 87 and 17 microg/ml, respectively, after secretin stimulation (p = 0.033). Statistically significant correlations were found between [PE-1] and peak [lipase] (r = 0.83, P < 0.001), as well as [PE-1] and peak [HCO3(3)-] (r = 0.65, P = 0.037). Conclusions are as follows: (1) PE-1 concentrations can be measured from duodenal fluid obtained by endoscopic aspiration. (2) Duodenal fluid PE-1 concentrations are decreased in CP compared to HS. (3) Duodenal fluid [PE-1] has an excellent correlation with [lipase] and therefore is a marker of acinar cell function. (4) Secretin-stimulated endoscopic function testing with measurement of bicarbonate and PE-1 may provide a simultaneous assessment of both ductal cell and acinar cell function.