During the years 1968 to 1973 70 patients suffering from malaria were admitted to one hospital in England. Twenty had malignant tertian malaria while the remainder had infections caused by Plasmodium vivax, P. ovale and P. malariae. Malaria should be suspected in every febrile patient who has visited a tropical country, and the diagnosis can be confirmed only by examining blood films. Disseminated intravascular coagulation may complicate the disease, and should be considered in every case.British workers spending short periods in malarious areas and Asian immigrants returning home for a holiday are often inadequately instructed about malarial prophylaxis, particularly the need to continue this for at least a month after they return home. Companies and travel agencies should be obliged to provide such instructions.