In the United States (US), travelers who have had malaria or who have taken antimalarial chemoprophylaxis are deferred as blood donors for 3 years to prevent transfusion-transmitted malaria. To assess the impact of shortening this 3-year exclusion period, national malaria surveillance data from 1972 to 1988 were reviewed. The average annual rate of transfusion-transmitted malaria is 0.25 cases per million units of blood collected. Of 45 reported cases, 38 percent were caused by Plasmodium malariae, 29 percent by P. falciparum, 24 percent by P. vivax, and 9 percent by P. ovale. Thirty-two donors were implicated in 34 cases of transfusion-transmitted malaria. Of 30 implicated donors whose native country was identified, 23 (77%) were foreign nationals and 7 (23%) were from the US. In a review of all imported malaria cases by species and by interval between date of entry and onset of illness, 98 percent of P. falciparum, 86 percent of P. malariae, 76 percent of P. vivax, and 74 percent of P. ovale infections became symptomatic within 6 months of the patient's arrival in the US, regardless of the use of prophylaxis. Shortening to 6 months the donor exclusion period for US travelers to malarious areas would result in a minimum of 70,000 additional blood donors' being made available, with a maximum annual increase of 0.03 additional cases of transfusion-transmitted malaria. The potential benefit of bringing healthy travelers back into the donor pool after a shorter period of exclusion merits consideration by the blood banking industry.