Abstract. The artemisinin derivatives are now used widely in areas with multidrug-resistant Plasmodium falciparum malaria such as Southeast Asia, but concerns remain over their potential for neurotoxicity. Mice, rats, dogs, and monkeys treated with high doses of intramuscular artemether or arteether develop an unusual pattern of focal damage to brain stem nuclei (particularly those involved in auditory processing). To investigate whether a similar toxic effect occurs in patients treated with these compounds, clinical neurologic evaluation, audiometry and early latency auditory evoked responses were measured in a single-blind comparison of 79 patients who had been treated with Ն2 courses of oral artemether or artesunate within the previous 3 years, and 79 age-and sex-matched controls living in a malaria-endemic area on the northwestern border of Thailand. There were no consistent differences in any of these test results between the cases and controls. This study failed to detect any evidence of significant neurotoxicity in patients treated previously with oral artemether or artesunate for acute malaria.Artemisinin derivatives are now used widely for the treatment of Plasmodium falciparum malaria in Southeast Asia. On the western border of Thailand where P. falciparum has developed resistance to nearly all antimalarials, the combination of mefloquine and artesunate was introduced in 1994 as a first-line treatment. 1 More than 3,000 patients with uncomplicated falciparum malaria have been recruited subsequently in prospective studies to optimize antimalarial treatment. Detailed prospective follow-up of these patients, including simple neurologic examinations, has failed to identify any serious adverse effects associated with the 2 most widely used compounds, oral artesunate or artemether. 2 However, animal studies have raised concerns about the potential neurotoxicity of some of the artemisinin derivatives. [3][4][5][6][7][8] These studies showed that rodents, dogs, and monkeys treated with intramuscular arteether or artemether (the 2 oil-soluble derivatives) develop dose-dependent damage to certain brain stem nuclei. Neurologic findings included gait disturbance, loss of spinal, brain stem, and pain responses, and, eventually, death. Pathologic changes in these experimental animals were found even in the absence of any detectable neurobehavioural symptoms. 4,5 The neuropathologic lesions were unusual in that they were confined to the neuronal cells of certain brain stem nuclei, whereas adjacent nuclei were often unaffected. The nuclei affected included those in the auditory relay. 6,7 Despite the lack of reported toxicity in extensive clinical studies to date, 2,9 it remains possible that the artemisinin compounds produce a similar pattern of neurotoxicity in humans. To assess possible toxic effects on the brain stem in patients treated with repeated courses of artemether or artesunate, brain stem auditory evoked responses (BAERs) were measured in a case-control study. These have been used 10 to detect neurotoxici...