The clinical relevance of the 13C-starch breath test was evaluated in comparison to the secretin-caerulein test as the "gold standard" of pancreatic function testing, fecal elastase concentration, and fecal chymotrypsin activity in 30 patients with mild (n = 15) or severe (n = 15) exocrine pancreatic insufficiency. 23 patients with gastrointestinal diseases of non-pancreatic origin and 31 healthy volunteers served as controls. 50 g of natural starch of maize were orally administered after a 12-h fast and breath samples were taken before and in 30 min intervals for five hours after oral ingestion and the increase of 13C/12C-isotopic ratio was analyzed by mass spectrometry. Specificity of fecal elastase (93%) and fecal chymotrypsin (93%) for impaired pancreatic function were much higher compared to the various parameters of the 13C-starch breath test (69-74%). Sensitivities of the 13C-starch breath test for all and separately for mild and severe exocrine pancreatic insufficiency were higher (total 70-77%) compared to fecal chymotrypsin (total 60%), but lower compared to fecal elastase (total 93%). With regard to the higher sensitivity and specificity, the higher practicability, and the lower costs determination of fecal elastase concentrations is superior to the 13C-starch breath test and therefore remains to be the most reliable indirect pancreatic function test available today.