Vasopressin (VS) has been reported to stimulate colonic peristalsis in different therapeutic conditions. In order to determine the mechanisms involved in this effect, colonic function was studied with three different techniques staying: a) the transit time of radioopaque markers through the colon was measured in 7 healthy subjects after VS IM (0.3 U/kg of weight). A marked propulsive effect was observed. One hour after injection, 64.7 +/- 16.2 p. 100 of the markers (m +/- sem) had left the right colon vs 9.1 +/- 4.6 p. 100 after injection of NaCl (p less than 0.01) and 70.5 +/- 10.8 p. 100 of the markers emptied from the left colon vs 4.3 +/- 4.5 p. 100 after NaCl (p less than 0.01); b) an electromyographic study was carried out in 6 other healthy subjects with an intraluminal device equipped with contact electrodes, introduced into the left colon by colonoscopy. The injection of VS was followed by an increase in the number of the propagating electrical spike bursts that are known to correlate well with the propulsion of the colonic intraluminal contents. The number of bursts was 2.7 +/- 0.6 bursts/30 min after NaCl and 5.2 +/- 1.4 bursts/30 min after VS (p less than 0.02); c) finally, the outflow of ileostomies and colostomies was measured in respectively 3 and 8 subjects over one h after IM 0.3 U/kg of VS. A considerable increase in the outflow of intestinal fluids was observed: output from the colostomies was 10 +/- 10 ml/h after NaCl and 250 +/- 39 ml/h after VS (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)