More than 40 cases of feline leishmaniasis have been reported in the scientific literature. The influence of some immunodepressive conditions of viral origin, such as leukemia and feline immunodeficiency, are still unknown. The purpose of this study was to assess the prevalence of Leishmania infection in cats and possible relations with these viral infections. Markers of Leishmania infection were searched in 183 cats from Southern Spain by IFAT, PCR, Giemsa stain and culture, with a follow-up of positive cats. Seropositivity was 60.0% (Ab titer > or =10) and 28.3% of animals presented Ab titers > or =40. Around 25.7% of the cats studied were parasitemic and some of them remained positive for months. Combining both data, 70.6% of the feline population was, or could be, infected. We observed a negative association between seropositivity to Leishmania and infection by FeLV. Hence, production of antibodies against the parasite appears to be compromised in cats with leukemia, which have a prevalence of 36% in our study. In contrast, we found no association with feline immunodeficiency. The results makes us doubt the value of conventional serological methods to detect active Leishmania infection in cats.