The validation of a simple and rapid DNA solubilization procedure is described. Quantitative extraction of intact, polymerized DNA was achieved by cell lysis or tissue homogenization in an ammonium hydroxide-Triton X-100 solution. The solubilization procedure inactivates endogenous DNAase and increases the fluorescence-enhancement activity of the extracted DNA, thereby eliminating the need for enzyme treatment or exposure to high salt solutions. The extracts can be utilized directly in a sensitive fluorescence-enhancement assay with bisbenzimidazole (Hoechst 33258) reagent. Estimates of DNA cell content were unaffected by the number of cells lysed or the volume of lysate employed in the assay. In all cases, the solubilized DNA estimates were linear and parallel to the bovine DNA standard. The optimum range for estimation of DNA in this assay is 5-150 ng. In addition, estimates of DNA obtained with this method and the standard diphenylamine assay were in excellent agreement. This simple, one-step DNA extraction procedure can be utilized in conjunction with Hoechst reagent to obtain quantitative estimates of DNA levels in cell or tissue extracts.