The Memorandum reviews the considerable progress that has been made in research on the chemotherapy of leprosy during the last 10-15 years, as a result of which it is now possible to study the same topics in leprosy as are studied in other bacterial diseases. Thus drugs have been screened in mice for their activity against Mycobacterium leprae. Those that have been found to have the greatest activity against M. leprae at acceptable dosages-dapsone, rifampicin, and clofazimine-have been characterized in terms of the minimal effective dosage and rate of bacterial kill. Similarly, their pharmacokinetics in man and in certain animals have been defined. The theoretical basis for drug trials in leprosy patients is discussed in terms of the number of viable and the number of dead M. leprae that remain at various stages of therapy. * This Memorandum was drafted by the signatories listed on page 432, who were the members of the Committee on Experimental Chemotherapy held at the Xth International Leprosy Congress,