Detection of Salmonella typhi in blood by culture of the mononuclear cell-platelet layer was compared with other methods currently used for the diagnosis of typhoid fever. Colonies of S. typhi were present in all mononuclear cell-platelet layer-positive cultures within 18 h of plating and were identified within an additional 10 min by a coagglutination technique. In contrast, identification of all positive cultures by conventional blood culture required 3 days.