The number, volume, and size of zymogen granules in pancreatic acinar cells of normal and streptozotocin-diabetic rats were measured using stereological techniques. These morphometric data were then correlated with the amylase activity of the acinar cells. In the normal rats, the acinar cells had a mean volume of 1,253.5 Km' and contained 343 zymogen granules, which occupied a volume of 103 pm' of the cell (8.28%). In the diabetic rats, the mean acinar cell volume was estimated as 1,017 km3 and the cell contained 220 zymogen granules, which occupied a volume of 55.8 pm' (5.38%). The cell volume and zymogen granule number and volume were 19, 36, and 46%. respectively, more in normal rat pancreas, while no difference in the size of zymogen granules