α-Difluoromethylornithine (DFMO; eflornithine), an inhibitor of polyamine biosynthesis, was used to treat 14 patients with late stage gambiense sleeping sickness, 12 cases having been previously treated with and considered refractory to melarsoprol. α-Difluoromethylornithine was administered intravenously at a dose of 400 mg/kg/day for 14 days followed by oral treatment, 300 mg/kg/day, for 21–28 days. In all patients treatment was associated with rapid disappearance of trypanosomes from body fluids (in several cases within 24 hr) and decreased cerebospinal fluid white blood cell counts. In all but one patient, who died of a pulmonary infection during treatment, α-difluoromethylornithine produced a dramatic reversal of clinical signs and symptoms of the disease. Determination of drug concentrations in serum and cerebrospinal fluid of 5 patients demonstrated that α-difluoromethylornithine diffuses into the central nervous system with cerebrospinal fluid levels representing up to 51% of corresponding serum concentrations. Diarrhea, abdominal pain, and anemia were the most frequent side effects associated with therapy, but were reversible and did not necessitate discontinuation of treatment. Four patients have been followed for more than 2 years post-treatment without evidence of relapse.