Abstract
Application of a fluorescence technique for the detection of the human Y chromosome in interphase nuclei indicates that the best results may be obtained from the study of lymphocytes in blood smears. The most satisfactory Y-fluorescence is obtained with the use of buffered quinacrine mustard dihydrochloride. The method can be complemented by other standard techniques to obtain a clear idea of the sex-chromosome complement of the individual. The application of this technique to clinical and chromosomal diagnosis and to the prenatal detection of the Y chromosome in amniotic cells seems at least as promising as has proved the earlier identification of the Barr body.