Melarsoprol is the most commonly used product for the treatment of patients suffering from human African trypanosomiasis (HAT) in the meningoencephalitic (second, late) phase. This treatment is frequently complicated by fatal reactive encephalopathy, and at the same time resistance is beginning to appear in various countries. Eflornithine is effective and better tolerated, but it is more difficult to use. Nifurtimox, registered in several South American countries for treatment of Chagas' disease but used off label since the 1970's in series of cases of meningo-encephalitic HAT, is at present the only other potential alternative for the treatment of late-stage HAT.