Over a period of more than 10 years we have isolated and classified 161 Leishmania strains from cases of human visceral, cutaneous and mucosal leishmaniasis in immunocompetent subjects, from cases of visceral leishmaniasis in immunocompromised individuals with HIV, from dogs with leishmaniasis (visceral and cutaneous), from Rattus rattus and from sandflies. The strains were all L. infantum, the only species endemic in Spain, and corresponded to 20 different zymodemes. We describe the life cycle of these zymodemes for which, in most cases, we only partially know the hosts involved. We also discuss possible reasons for the greater polymorphism of L. infantum in southern Spain.