Abstract: Nucleic acids in non-rare cells in a sample containing non-rare cells and rare cells are selectively released from the non-rare cells. The sample is combined with an aqueous medium, and the combination is held for a period of time and at a temperature for selectively releasing nucleic acids from the non-rare cells but not from the rare cells. The sample is subjected to filtration to separate rare cells from non-rare cells. Rare cells with intact nucleic acids are separated from non-rare cells and nucleic acids from the non-rare cells. Nucleic acids from the rare cells are subjected to one or more identification techniques either with or without extraction of nucleic acids from the rare cells.