The paper by Randrianarivelojosia and colleagues in this issue of the Journal (p. 47) describes the in vitro susceptibility of Plasmodium falciparum in Madagascar and the Comoros Union to three of the commonly used antimalarial drugs in the region — quinine, mefloquine and cycloguanil (the active metabolite of proguanil). Severe malaria in the Comoros Union and in Madagascar is invariably caused by P. falciparum, as it is in the rest of sub-Saharan Africa. All of 243 isolates assessed were sensitive to quinine, the drug recommended throughout the region for treatment of severe malaria. With regard to the two chemoprophylactic agents studied, all 67 isolates assessed were sensitive to cycloguanil and only 1 of 128 isolates was mefloquine-resistant. The mefloquine-resistant isolate was 1 of 110 evaluated from Madagascar; none of the 18 isolates from the Comoros Union was resistant. The authors argue that their findings confirm the sensitivity of the parasite to the 3 drugs most commonly used in their countries for both treatment and prophylaxis. They submit, on the basis of their findings, that current policy for treatment of severe malaria with a 7-day course of quinine, and prophylaxis with either mefloquine or cycloguanil-based regimens, is justified by the in vitro laboratory findings that they have shown.