Samples of blood from pet cats were examined for evidence of feline leukaemia virus (FeLV) by three techniques: virus isolation, immunofluorescence and an enzyme-linked immunosorbent assay (ELISA) Leukassay F. There was good agreement between the results from virus isolation and immunofluorescence. However, about 30 per cent of cats which were positive for FeLV antigen by ELISA were negative by either of the other tests. The status of most of these cats was unchanged four or 12 weeks later.