Determination of the fraction of G0 cells in cytologic samples by means of simultaneous DNA and nuclear protein analyses.

The ratio of protein to amount of DNA in the nucleus was cytophotometrically determined by means of a combined Feulgen-naphthol yellow S staining procedure. Quiescent normal lymphocytes, bronchial epithelial cells and mammary epithelial cells all showed ratios that were significantly lower than in the proliferating counterparts of the different cell types. Hence, combined determinations of DNA and nuclear protein make it possible to determine the fraction of growth-arrested cells (G0 cells) in cytologic preparations.