The seroprevalence of feline immunodeficiency virus (FIV) in 203 apparently healthy domestic cats living in the district of Pisa, central Italy, was 11·3 per cent, and the prevalence of feline leukaemia virus (FeLV) was 8·4 per cent. The prevalence of FIV depended significantly on the lifestyle and age of the cats; cats living outdoors were more likely to be FIV-positive than cats living indoors, and the proportion of FIV-positive cats increased with age. In contrast, there was no significant relationship between these variables and the prevalence of FeLV. There was no significant relationship between the cats’ seropositivity for FIV and FeLV. The results of a five-year field study to control FeLV infection by vaccination in a colony of 30 domestic adult cats naturally exposed to the infection suggest that the vaccination was effective in FIV-negative cats, but failed to protect FIV-positive cats against FeLV.