Tuberculosis (TB) is a major cause of death, with 8 million new cases and 23 million deaths per year. Approximately one-third of the worlds population is infected with the bacterium responsible, Mycobacterium tuberculosis, and once infection is established the organism may persist indefinitely in a latent state. Of those who are infected, only ∼10% develop overt disease. This discrepancy between numbers infected and numbers who become ill is common to many infectious diseases and likely represents differences in the balance between host defences and the virulence of the organism. We investigated if a genetic factor, the gene for apolipoprotein E (APOE), is involved in the response to M. tuberculosis.