Trials of immunization against Leishmania tropica were initiated in the Israel Defense Forces in 1968. The rate of takes declined gradually over the years. In 1975, 425 soldiers were inoculated with the same strain of L. tropica as that used since 1968; they were examined at 3- and 6-mo. intervals after the inoculation, with 291 soldiers undergoing at least 1 follow-up examination. Only 13.7% developed lesions at the inoculation site, usually 3-6 mo. after inoculation. Leishmanin tests were performed in 220 soldiers and there were positive reactions in 19.5%. There was a fair correlation between the development of clinical lesions and positive leishmanin tests. A positive leishmanin test, and/or a typical lesion were seen in 21.3% of the inoculated soldiers. L. tropica tends to lose its virulence after prolonged storage and multiple passages. A new strain isolated a few months before this trial was used to inoculate 50 soldiers, 31 of whom were followed-up. All 31 developed typical lesions at the site of inoculation, most of them within 2-4 wk following inoculation.