From 1980 to 1987 ileoanal pouches were made in 83 patients. Specimen for a set of laboratory analyses were taken preoperatively, during the ileostomy and loop ileostomy periods and repeatedly during 36 months of follow-up. Cobalamine absorption and 14C-triolein breath tests were performed preoperatively in electively operated patients and postoperatively in all patients at 12 and 36 months. Low S-Ca was most pronounced preoperatively in patients who were to undergo acute colectomy (53%). Decreased S-Mg was detected in 16-36% at all stations. None had signs or symptoms of hypomagnesemia. Low S-albumin was rarely seen except for preoperatively in acute patients. Increased IgM was found in 40% of the patients during the loop ileostomy phase compared to 6-10% preoperatively. Substantially increased orosomucoid and/or haptoglobin were seen in patients during the functional periods but these increased values could not be correlated to episodes with acute pouchitis. High values of S-ALAT and ALP were much more frequent during the loop ileostomy periods than it was preoperatively and during pouch function. Low S-haemoglobin and/or iron were noticed during the functional period in 3-8% and 10-16%, respectively. Severe anaemia, due to iron deficiency developed in one patient after 2.5 years of pouch function. Preoperatively, slight decreases of S-B12 were found in 13% and impaired cobalamine absorption was revealed in 38% of the electively operated patients. The corresponding figures were 3% and 31% after 12 months and 5% and 36% after 36 months of follow-up, respectively. B12 substitution was given to in all 8 patients during the follow-ups. Lipid absorption was disturbed in 38% preoperatively and in 35% and 41% at 12 and 36 months, postoperatively.