The Invader® assay is a homogeneous, isothermal, signal amplification system for the quantitative detection of nucleic acids. The assay can directly detect either DNA or RNA without target amplification or reverse transcription. It is based on the ability of Cleavase® enzymes to recognize as a substrate and cleave a specific nucleic acid structure generated through the hybridization of two oligonucleotides to the target sequence. The combination of sequence-specific oligo-nucleotide hybridization and structure-specific enzymatic cleavage results in a highly specific assay well suited for discriminating closely related gene sequences. This includes detection of single nucleotide polymorphisms directly from genomic DNA as well as highly homologous mRNAs in closely related gene families. Because Cleavase® substrate recognition is structure, and not sequence dependent, cleavage and detection can be applied to virtually any DNA or RNA sequence.