EACH year, approximately 1 million Americans travel to countries where they may be exposed to malaria.1 Infections with Plasmodium falciparum in such travelers are of particular concern because these infections can be fatal.2 Use of effective chemoprophylaxis can reduce the risk of infection from malaria considerably.3 All travelers to malariaendemic countries are advised to take chloroquine each week as chemoprophylaxis. In addition, from 1982 until April 1985, the Centers for Disease Control (CDC) advised travelers to countries with chloroquine-resistant P falciparum to also take pyrimethamine-sulfadoxine each week.4 However, information on cases of malaria in the United States reported to the CDC suggests that use of chemoprophylaxis by US travelers is incomplete: only 28% of the 410 US patients infected with P falciparum in Africa between 1980 and 1984 had used a recommended drug regimen for prophylaxis, and none of the 58 patients with P falciparum infections