Aedes aegypti mosquitoes which were first allowed to feed on untreated lepromatous leprosy patients, and then to refeed on mouse footpads were found to transfer Mycobacterium leprae to the footpads as seen by the subsequent multiplication of the bacilli in the footpads. Results presently available are insufficient to come to any conclusion about the actual role of mosquitoes in the transmission of leprosy in the field.