Recent years have seen the introduction of a number of whole-blood assays, in which unseparated heparinized blood is stimulated with antigen either overnight or for as long as 6 days, and cytokine production is measured in the plasma or supernatant. These assays have potential for use in the field as immunodiagnostic assays, as they require only a small blood sample and basic laboratory facilities. Use of these assays in a large study of the immunological effects of BCG vaccination in Malawi has shown that the diluted blood, 6-day whole-blood assays is robust, and can be used to assess T-cell responses to both crude and recombinant antigens. If used with antigens specific to Mycobacterium leprae, these assays could be used to measure exposure of M. leprae within communities or populations, or to aid the early diagnosis of leprosy.