The novel antimalarial Ro 42-1611 (arteflene) was evaluated for safety and efficacy in an open, non-comparative study of patients with mild malaria in the south of Cameroon. Thirty male patients aged 12 to 42 years, with an initial Plasmodium falciparum count of > 5000 (mean: 21,406) parasites/microliters and a body temperature of 37.7% to 39.8 degrees C, were selected to receive a single dose of arteflene, corresponding to 25 +/- 2.5 mg/kg bodyweight. Efficacy was assessed at 6, 9, 12, 24, 36, 48 and 72 hours, and at seven days by: reduction in parasitaemia and time to parasite clearance; resolution of fever and clinical cure (defined as the absence of signs and symptoms of malaria). Adverse events were reported at baseline and at each assessment point, and laboratory tests were carried out at 2 and 7 days. The mean number of parasites/microliter fell from 21,406 at baseline to 157 after 48 hours, at which point 80% of patients were completely free of parasites. Mean body temperature was reduced from 38.9 degrees C at baseline to 37.3 degrees C 12 hours after arteflene administration, and by this time 80% of patients had a normal temperature. Clinical cure rates were also high, with 70% of patients free of all signs and symptoms after 24 hours. However, by day 7, 6/30 (20%) presented with smears positive for P. falciparum. There were no adverse events considered to be related to treatment. A single dose of 25 mg/kg arteflene was found to be an effective and well-tolerated treatment for mild P. falciparum malaria.