This is the first report on the determination of nucleic acids with Pyronine B (PB) sensitized by cetyltrimethylammonium bromide (CTMAB) with resonance light-scattering (RLS) technique. Under the experimental conditions (1 x 10(-5) mol l(-1) PB, 1 x 10(-5) mol l(-1) CTMAB, pH 7.4, at room temperature, ionic strength 0.02 mol l(-1) NaCl), the interaction of PB with DNA sensitized by CTMAB results in enhanced RLS signals at 328 and 377 nm in the enhanced regions. It was found that the enhanced RLS intensity at 328 nm was proportional to the concentration of DNA in the suitable ranges. The linear range of this assay is 0.0-1.2 microg ml(-1) for calf thymus, 0.0-0.8 microg ml(-1) for fish sperm DNA (fsDNA), and 0.04-1.4 microg ml(-1) for yeast RNA, respectively. The detection limits (3 sigma) are 6.1 ng ml(-1) for calf thymus DNA (ctDNA), 11.2 ng ml(-1) for fish sperm DNA, and 8.6 ng ml(-1) for yeast RNA, respectively. Six synthetic samples were determined satisfactorily. This method is simple, rapid and the dye is inexpensive and stable.