Sulfanilamide (1%) fed to rats and mice infected with the mouse strain of lepra bacillus throughout the whole of the exptl. period of 1 yr. completely inhibits the growth and development of the leproma at the site of inoculation and prevents the occurrence1 of distant metastascs. 1% sulfanilamide and in a single trial 1% sulfathiazole were found to arrest the further development of the leproma and its metastases when given after an untreated period of the infection. 1% sulfanilamide. given during the first part of the infection and then withdrawn, permits the inhibited lepromatous lesion to evolve again, but, more slowly than would be1 expected. One reason given for this is that large numbers of lepra bacilli "bottled up'''' within necroses of the: inhibited lesion are unavailable for further growth after withdrawal of the1 inhibitory agent. There is no indication, however, that, with inhibition of the lesion produced by the ehemotherapeutic agent, the lepra. bacilli are killed to any degree, as evidenced by the1 unrestricted growth of the leproma induced by these bacilli in a 2d host after being inhibited for a yr. in the primary treated host. In view of this and in the absence1 of any clear evidence that the1 bacilli, alive or dead, can be digested by the evils of the; host, the permanency and unaltered character of the inhibited lesion are understandable, as is its unfailing progression following removal of the1 inhibiting agent.