Two feline malignant lymphoma cell lines, FT-1 and FT-G, established from cats naturally infected with the feline leukemia virus were analyzed for chromosomal aberrations. Both FT-1 and FT-G cells had a modal number of 38 which is the normal diploid (2n) chromosome number of the domestic cat. G-banding-analysis showed that FT-1 had a translocation involving the short arms of chromosome A2 and D3--t (A2;D3) (p-;p+), and FT-G had a translocation involving the short arms of chromosomes A2 and B2--t (A2;B2) (p-;p+). Our data suggest that the chromosomal translocations were closely associated with the tumorigenesis in malignant lymphoma in cats.