Isoenzyme analysis, carried out on some hundreds of Leishmania isolates from the Mediterranean basin by specialized identification Centres, has provided new data on the taxonomy of this parasite in the area. Three complexes of zymodemes have been identified: L. infantum s.l., L. tropica s.l. and L. major s.l. L. infantum is the agent of human and canine visceral leishmaniasis and it is distributed throughout the Mediterranean area. Furthermore, this parasite is the only responsible for human cutaneous leishmaniasis in Central-Western Europe, including Italy. The distribution of L. tropica, agent of urban, or anthroponotic, cutaneous leishmaniasis, appears to be very limited, being restricted to Middle East, Tunisia and Greece. On the other hand, L. major, which causes rural, or zoonotic, cutaneous leishmaniasis, is widespread throughout North Africa and Middle East. In some countries, such as Tunisia and Israel, leishmaniases are caused by all the three complexes.