Chromosome changes in butylnitrosourea (BNU)-induced mouse leukemia

G-banding analysis was carried out in 45 mice after exposure to the leukemogen butylnitrosourea (BNU). Of 27 animals without clinical signs of leukemia, 2 had chromosomal rearrangements (7%) while, of 18 leukemic mice, 5 showed abnormal karyotypes (28%). The chromosomal abnormalities were not random and showed preferential changes of chromosomes Nos. 14 and 15. The organ distribution of the chromosomal abnormalities showed a preferential involvement of the thymus with a secondary presence of chromosome anomalies in peripheral lymphoid organs and the bone marrow. The findings are discussed in relation to the recent reports on the specificity of trisomy 15 in murine leukemia and lymphoma.