Technique for the visualization of exchange aberrations in human chromosomes.

A technique for the visualization of chromatid exchange in human chromosomes is described. Additon of the base analogue 5-bromodeoxyuridine (BUdR) into PHA stimulated lymphocyte cultures and subsequent staining with the benzimidazol compound "33258 Hoechst", and Giemsa, results in differential fluorescence or staining of sister chromatids in second division metaphases. This technique allows an accurate scoring of sister chromatid exchanges, and could be used in the evaluation of the effect of external agents on the induction of previously unrecognized chromatid exchanges in human chromosomes.