The aim of this study was to examine the relative importance of the enzymes ornithine decarboxylase (ODC) and diamine oxidase (DAO) in intestinal polyamine metabolism in normal rats. To study this we measured jejunal and ileal DAO and ODC activities and polyamine levels 2 h after injecting, in non-fasting male Wistar rats, either normal saline (controls) or a large dose of i.v. heparin to deplete intestinal mucosal DAO stores. We found that heparin significantly reduced mean DAO activity (p less than 0.001). As a result putrescine levels increased significantly in both jejunum (p less than 0.02) and ileum (p less than 0.01). Heparin-induced DAO depletion had no significant effect on spermine and spermidine levels at either site. The increased putrescine was associated with reduced ODC activity in both jejunum (p less than 0.01) and ileum (p less than 0.05). ODC activity correlated negatively with putrescine (p less than 0.001). These results suggest that (i) in normal rats, DAO is more important than ODC in regulating mucosal putrescine levels and (ii) putrescine exerts feedback inhibition of ODC.