We describe two cases of severe colonic pseudo-obstruction (Ogilvie's Syndrome) after high dose clonidine i.v. infusions for delirium tremens. The first symptoms occurred 36 h and 5 days, respectively, after institution of therapy. The diagnosis of colonic pseudo-obstruction (CPO) was confirmed during emergency laparotomy in both cases. While other known risk factors may have been present, we propose that clonidine had a major parasympatholytic effect on the large bowel of these patients and was therefore responsible, either alone or in combination with these other factors, for the development of CPO. We conclude that the therapy of delirium tremens with high i.v. doses of clonidine carries the risk of provoking severe CPO, especially when other contributing factors are present. While therapy of the alcohol withdrawal syndrome with clonidine appears to be an attractive alternative to conventional treatment, ICU physicians should be alerted to this potentially serious complication.