Early in 1941 a new drug, "promin," was introduced in the treatment of leprosy at the National Leprosarium. After several months' treatment of a few patients with this drug rather decided improvement occurred in their specific leprous lesions. In November 1943 the "promin" treatment of leprosy was first reported in the medical literature 1 and was regarded as the most encouraging experimental treatment ever undertaken at the National Leprosarium. Since then "promin" and its related sulfones, "diasone" and "promizole," have been used extensively in the treatment of leprosy with exceedingly good results. At the Second Pan-American Leprosy Conference held in Rio de Janeiro, Brazil, in October 1946, the Subcommittee on Therapeutics took cognizance of the divergent opinions on the effect of chaulmoogra oil and its derivatives in the treatment of leprosy. 2 The committee advised that the efficacy of chaulmoogra oil be reevaluated. Simultaneously, it recognized the sulfone drugs as