[Measurement of the DNA content in morphologically identified cells on a Wright-Giemsa stained smear]

4',6-Diamidino-2-phenylindole (DAPI) staining was applied to measuring nuclear DNA contents of single cells previously identified on a Wright-Giemsa stained smear. The smear was first photographed and the location of each cell was mapped. The smear was then destained with 50% acid ethanol and absolute methanol, and restained with DAPI (pH 7.4) at 4 degrees C. Blue fluorescence was observed in the nucleus, and the intensity of this fluorescence was proportional to the amount of DNA, with the lowest coefficient of variation of 3.6% in the case of staining the peripheral lymphocytes for 30 min. This method is useful for measuring DNA contents in heterogeneous cell populations.