To provide revised guidance on malaria prevention for the medical advisers of travellers from the United Kingdom going overseas to malarious areas, a committee of those most involved in giving advice and with specialist expertise in the United Kingdom agreed a policy document. There is a need for all travellers to be aware of the risk of malaria and to take measures to avoid being bitten by anopheline mosquitos, especially at night. Chemoprophylaxis is recommended also for most malarious areas. In view of the increasing prevalence of strains of Plasmodium falciparum resistant to chloroquine and proguanil, mefloquine is added to the list of recommended drugs for more areas than in the past, and is the preferred chemoprophylactic for east and central Africa. Chloroquine with proguanil continues to be widely appropriate. Detailed recommendations are given for each country. Travellers out of reach of prompt medical assistance are advised to carry treatment doses of a standby drug: halofantrine, Fansidar, or quinine. The need for full compliance with any regimen is emphasised. No prophylaxis is totally effective. Malaria must be considered in the differential diagnosis of any fever in someone who has visited an endemic area within the past year.