Chemoprophylaxis and malaria in American servicemen returning from Vietnam.

Information relating to chemoprophylaxis and malaria in 49 men who served with the United States Armed Forces in Vietnam and who developed overt malaria after departure from Vietnam indicated that: 1) compliance with intended chemoprophylactic regimens was far optimal; 2) a history of recent prophylactic ingestion of chloroquine was not a reliable indicator of infection with chloroquine-resistant Plasmodium falciparum: 3) reported ingestion of half or more of an intended terminal chemoprophylactic regimen was associated with a prolongation of the time that elapsed before initial post-departure episodes of vivax malaria; and 4) such partial compliance with intended terminal chemoprophylaxis may have been associated with a decreased incidence of second post-departure episodes of vivax malaria.