The diagnostic efficacy of bone-marrow culture, serial blood cultures and agglutination tests was compared in a prospective study of 60 patients with typhoid fever, two thirds of whom had received prior antibacterial therapy. Salmonella typhi was recovered from marrow cultures in 95% of patients but blood cultures were positive in only 43.3% (P< 0.001). Agglutination tests were eventually diagnostic in 56.7% of patients, but in only 25% at the time of admission. If procedures had been limited to blood cultures and agglutination tests, diagnosis would have been missed in 21.7% of cases. The efficacy of marrow cultures was affected not by the duration of disease but by the extent of antibacterial therapy before presentation. Bacteriological recovery was faster from marrow cultures.