A dosage of 4 mg/kg/day intravenous cyclosporine as an adjunct to high-dosage hydrocortisone has been recommended to avoid colectomy in acute steroid-resistant ulcerative colitis. In treating eight such patients, four of whom presented with toxic megacolon, we immediately tapered the steroid dosage and infused a lower dosage of only 2 mg/kg cyclosporine for 15 days to fit a therapeutic range of 60-240 ng/ml, as previously designed for a kidney transplant program. Seven of the eight (87.5%), including three with megacolon, went into remission and started the chronic phase of treatment; the eighth patient underwent colectomy. Of the seven, one died on day 3 of the chronic phase because of pulmonary embolism while in clinical remission, and another discontinued treatment. The other five (62.5%) remain in remission on 6 mg/kg oral cyclosporine, or have already switched from cyclosporine to azathioprine. Two episodes of reversible nephrotoxicity appeared in the chronic phase only. These results emphasize the efficacy and safety of cyclosporine in acute ulcerative colitis, but there is still a need for further dose-response and drug association relationship studies.