At week 20 post-challenge, cats of groups 10K and 100K were euthanized and different tissue samples were collected and analysed for the presence of FeLV DNA sequences. Popliteal and mesenteric lymph nodes, bone marrow, spleen, kidney, urinary bladder, lungs, thymus, myocardium, parotid gland, and pancreas were tested. FeLV DNA sequences were found in organs of the cat (JCR2) positive for FeLV provirus in blood. The copy numbers were in average very low and ranged from 5.6 to 704.25 copies/reaction (3.4 · 10 À5 to 0.0024 copies/cell, data not shown). The popliteal lymph node showed the highest FeLV proviral load (0.0024 copies/cell). No FeLV DNA sequences were detected in tissue samples of all other cats. Virus isolation from urinary bladder, myocardium, lungs, mesenteric lymph node, thymus, and bone marrow was negative for all cats. 