AbstractWe examined the effects of bowel manipulation on mast‐cell number and function in the rat. Mast cells were assessed histologically and by their ability to induce muscle contraction. Anaesthesia or abdominal incision did not alter mast‐cell number. However, laparotomy plus brief exteriorization of jejunal segments significantly increased mast‐cell number. Applying saline to the serosal surface by swab or droplet application increased mast‐cell number 16‐ and 3‐fold, respectively. Saline swabbing of jejunal segments from rats previously infected with Trichinella significantly reduced mast‐cell number. Functional integrity of mast cells was illustrated by muscle contraction in vitro following compound 48/80 or antigen and inhibition of cromoglycate. Serosal application of compound 48/80 in vivo increased mast‐cell number. This increase in mast‐cell number by compound 48/80 or by saline was prevented by prior treatment with cromoglycate. These data suggest that mast‐cell degranulation underlies the manipulation‐induced masto