Effect of azathioprine on the chromosome complement of human bone marrow cells

Chromosome studies were performed on bone marrow aspirates from 15 patients treated with azathioprine. In most patients the immunosuppressive therapy produced structural changes of the chromosome complement. The structural chromosome aberrations disappeared after cessation of therapy. In four patients no evidence of chromosome abnormalities could be found during therapy with azathioprine. It is proposed that the study of bone marrow cells may be more important than that of short‐term leukocyte cultures when estimating the chromosome damaging properties of some chemical agents.