The effect of cyclophosphamide and isoniazid (INH) alone and in combination on the centromere separation sequence in Chinese hamster bone marrow cells.

X-irradiation of Chinese hamsters with 50 and 200 rad delayed the centromere separation of bone marrow chromosomes. Combination of a treatment with 13.3 mg cyclophosphosphamide/kg body wt. and 50 rad did not result in an enhanced effect compared with the single treatments. Again, the separation sequence was not influenced. No delay was induced by a treatment with 125 mg isoniazid/kg, but a slightly and significantly earlier separation of the chromatids in both groups of metacentric and acrocentric chromosomes occurred. The separation delay seen after irradiation with 50 rad disappeared when the animals were pretreated with isoniazid. Independently of these results the asynchronous separation sequence was not altered in any of the experiments.