Primary dapsone resistance as assessed by uptake of labelled thymidine by the macrophage resident Mycobacterium leprae.

12 untreated lepromatous leprosy patients were screened for primary dapsone resistance by the uptake of labelled thymidine by macrophage resident M. leprae. There were found to harbour primary dapsone resistant strains of M. leprae and another three partially resistant strains to the drug. This rapid, simple and reliable method should be used routinely to screen leprosy patients, for drug resistance.