New tools are desirable to examine the metabolic state of individual cells within tissues. We proposed a fluorescence-based procedure consisting of acridine orange staining and fast green counterstaining (AO-FG) to improve the selectivity of the former for nucleic acids (acridine orange stains both DNA and RNA with different fluorescence colors), with no interference from proteins. We compared this test with the biochemical quantification of the relative amounts of RNA and DNA in selected rat ventral prostate samples and PC3 cells. The epithelium of the prostate gland is highly active metabolically for the production of secretions. Differences in AO-RNA staining were revealed and correlated with the metabolic state of the epithelium. Specificity was confirmed by RNase A. To assess how AO-FG staining correlates with the metabolic state of the cell, we cultured PC3 cells in different concentrations of glucose and measured the ratios between the amounts of RNA and DNA. In parallel, similar cultures were subjected to AO-FG, and the staining pattern correlated closely (r2=0.886) with the obtained biochemical results. The results confirmed that the combined use of AO and FG is useful for detecting DNA and RNA simultaneously, as well as for assessing quantitatively the transcriptional activity of individual cells and their changes in response to experimental manipulation.