Abstract. 2 of 31 subjects with no previous history of exposure to Leishmania tropica were found to have a positive leishmanin skin reaction. No cutaneous lesions developed in 30 adults following vaccination with a 5 year-old human strain of L. tropica isolated from Yotvata, in the Negev of Israel. Revaccination of 24 of these subjects with a strain isolated from Jericho was successful in all. The possible importance of the origin of the strain with regard to maintenance of infective potential is discussed.