Method of preparing a biological sample appropriate for use in a subsequent in vitro nucleic acid amplification reaction. The method involves a rapid, transient exposure to alkaline conditions which can be achieved by mixing an alkaline solution with a pH-buffered solution that includes a detergent and the biological sample to be tested for the presence of particular nucleic acid species using in vitro amplification. The invented method advantageously can improve detection of some target nucleic acids without substantially compromising detectability of others. The method is particularly useful for simultaneously preparing RNA and DNA templates that can be used in multiplex amplification reactions.