Since some previous studies have reported elevated total serum IgE levels in leprosy, that may be associated with the existence of a state of generalized T cell anergy, we undertook a carefully controlled study of this immunoglobulin in such patients before and after treatment with a Mycobacterium leprae-BCG vaccine. We found, firstly, that lepromatous leprosy patients suffering active disease had only a moderate elevation of IgE levels that was not statistically significant when compared to appropriate controls. In addition, multiple injections of the vaccine did not cause alterations in the concentration of this immunoglobulin. We were, therefore, unable to confirm the possible existence of a generalized immunodeficiency in lepromatous leprosy that could cause hyper-production of IgE.