Transfusion-induced malaria is a problem because of the large number of parasites infused and the weakness of transfused patients. Screening of blood donors or treatment of transfused patients or prospective donors does not eliminate this hazard. It is essential to kill the parasite in vitro in the blood of donors before transfusion. A total of 4,484 blood donors were screened for malaria parasite microscopically using the Giemsa staining technique. Only 30 matched the inclusion criteria of this study. Blood samples were divided into four equal samples. Three concentrations of sulfadoxine-pyremthamine (SP) were added to 90 specimens, and none was added to 30 specimens (controls). Blood specimens were then tested by parasitic, biochemical, and hematologic techniques on the day of collection and after 24 and 48 hours of storage in a blood bank refrigerator. The reduction of malaria parasites was proportional to the concentrations of SP and to the storage period. Blood samples without SP had steady number of the parasites. The lethal dose of SP (the dose that killed 99% of the malaria parasites within 24 hours) was 179.65 mug/L and was highly effective within the 24-hour storage period. This dose did not affect constituents of the stored blood. Thus, for eradication of transfusion-induced malaria by in vitro processing of donors blood, SP is a safe and effective drug. It is recommended that optimal doses of SP be added to donated blood prior to phlebotomy.