Viable pancreas fragments from five human donors were incubated in oxygenated buffered Eagle Medium. The preparation and incubation conditions were based on the method of Scheele and Palade. In Group 1 there was 1-h preincubation with echothiophate (10(-4) M); then, acetylcholine (10(-5) M) was added. After 2 h tissues were prepared for electron microscopy. Acinar injury with vacuole formation was apparent. Many of these changes were observed in fragments incubated only with acetylcholine (10(-5) M) (Group 2) and in incubates with echothiophate only (10(-4) M) (Group 3); only minor changes were seen in controls with Eagle's Medium (Group 4). Large vacuoles were significantly more numerous in Group 1 than in Control Group 4 (p < 0.05). Zymogen granules were depleted in Groups 1, 2, and 3. This depletion was significant in Group 1 when compared with Group 4 (p < 0.02). These results extend previous in vitro results that showed increased amylase release after echothiophate treatment in human pancreas and a left shift in response to acetylcholine.