Abstract
We describe a new staining technique (H-Ag-S) which allows observation and counting of active nucleolus organizer regions (NORs) and evaluation of the amount of DNA in the same cell nucleus. The procedure consists of combining a modified AgNOR staining method with the Feulgen reaction. A sequential procedure is proposed, based on the determination of optimal staining conditions. The technique, which was designed to allow studies of correlations between the transcriptional activity of rDNA genes and the cell ploidy, was primarily developed for rat liver smears. It should be applicable to most biological preparations, but the optimal conditions might be variable.