Visceral leishmaniasis (VL) is one of the most important parasitic diseases which are endemic in different parts of Iran. Serological studies were conducted by direct agglutination test (dat) on 12144 human serum samples, collected from four geographical zones of Iran. Sero prevalence, geographical distribution, clinical signs and symptoms for human visceral leishmaniasis based on dat for the period of 2002 through 2005 were determined. From 516 kala-azar cases detected: 50.6% were from Meshkin-shahr and Moghan districts in Ardabil Province, northwest of Iran and 49.4% were detected from other areas of Iran. In physical examination of seropositive cases, which were detected by dat with anti leishmanial antibodies at titers of 1: 3200 to 1: 102400, almost 50% of suspected individuals showed the classical kala-azar signs and symptoms. Predominant signs and symptoms in 233 hospitalized patients with anti-Leishmania antibodies at 1:3200 and higher, were fever (88.0%) and splenomegaly (84.5%). Statistically significant difference was found between males (58%) and females (42%) (P< 0.01). Moreover, 93.6% of the VL patients were £ 5 yr of age, and 6.4% were older than 5 yr that this difference was statistically significant (P< 0.01). From 1383 serum samples collected from domestic dogs in the villages that are known as endemic foci of human leishmaniasis, 152 (11.0%) were positive by dat (³ 1:320). Parasitological and serological examinations that were performed in 30 wild canines showed that 10% of these animals were infected by L. infantum. L. infantum Lon 49 is the principal agent of the disease in human as well as animal reservoir hosts in different parts of Iran. For the first time in Iran, L. tropica isolated from both skin lesions in the face and bone marrow aspiration in a HIV+ man who co infected with VL as well as in an infected dog from Ardabil Province.