After massive resection of the small intestine the remnant mucosa has an important capacity to enlarge the absorptive surface for the digestion, hydrolysis and absorption of nutrients. This intestinal adaptation is achieved by the interaction of various factors. Oral nutrients together with pancreatic biliary secretions stimulate the mucosa to become hyperplastic. Secondary to these luminal factors hormones play an important role in the adaptive process. Among the hormones, enteroglucagon is the most important growth promoting agent together with other growth factors such as epidermal growth factor, prostaglandin E2 and human growth hormone analogues, e.g. plerocercoid growth factor from the plerocercoid larvae of the tapeworm Spirometra mansonoides. The intestinal enterocyte is the target of these factors and within the cell the synthesis of polyamines, which are responsible for rapid growth, is the most essential step for the development of hyperplasia after resection. The rate limiting enzyme for polyamine synthesis ornithine decarboxylase (ODC) reacts to trophic stimuli with an increased activity. Thereafter rapid accumulation of tissue polyamines occurs. Blockade of ODC by specific inhibitors is accompanied by absence of intestinal hyperplasia after resection. Therefore it is concluded that ODC plays a key role in the intestinal adaptation of the remnant small bowel. To start and enhance intestinal hyperplasia after resection in patients with short bowel syndrome introduction of oral nutrition as soon as possible after operation is very important. On account of gastric acid hypersecretion the use of H2 receptor blocking agents is recommended. A decreased intestinal transit time is treated with loperamide.(ABSTRACT TRUNCATED AT 250 WORDS)