While there are several reports of prostaglandins of the E series being associated with increased mucosal mass in the stomach, their effects on the small intestine are less well documented. A microdissection-based technique was used to measure proliferation and crypt size in the duodenum, jejunum and ileum of dogs given the prostaglandin analogue misoprostol. Six test and six control animals were given an oral dose of 300 micrograms kg-1 day-1 of misoprostol for 11 weeks, a dose-duration combination chosen to optimize the development of gastric hyperplasia. Misoprostol increased both the area of the crypts (P less than 0.001) and the number of mitoses per crypt (P = 0.002) throughout the small intestine. The technique also demonstrated a significant gradient in crypt size and in crypt area from the duodenum to the ileum. There was no statistical interaction between misoprostol and the site studied, suggesting that this trophic effect was systemic or systemically mediated.