Three Leishmania strains of the old world were the subject of this study. Both the amastigote and promastigote stages were subjected to staining by Feulgen procedure and examined by computerized image analyser system to determine their nuclear DNA content. Results of this study showed that, in the promastigote stage there is a single cell population, whereas in the amastigote stage there are two population of parasite nuclei. One with low level of DNA resembling that of the promastigote and a second population with double DNA level. This latter formed when apparently 2 nuclei fused and form one with double DNA level. The data obtained in the present study further indicate that Leishmania of the old world can undergo nuclear fusion which is a strong evidence for the presence of sexual reproduction in the parasite.