Multidrug-resistant falciparum malaria is a major health problem along the Thai-Burmese border. From July 1985 until December 1986 a total of 5192 patients with falciparum malaria (1734 males, 3458 females) from this area were given supervised treatment with the combination mefloquine-sulfadoxine-pyrimethamine (MSP). The radical cure rate, assessed 21 days after drug administration, was 98.4% for the first 1975 patients, and 98.8% when assessed at 28 days for the remaining 3217 patients. In 3...