A major limitation of gene expression profiling using microarrays has been the substantial amount of RNA required for standard probe labeling techniques, especially when working with clinical samples such as biopsies, microdissected tumors, and laser-captured cells. CLONTECH's PCR-based SMART technology (Switch Mechanism At the 5'end of RNA Templates) bypasses this problem by allowing accurate cDNA amplification from nanogram quantities of total RNA. This amount of RNA ensures that SMART amplification yields a pool of cDNA, which reflects the sample's original complexity and relative abundance of the original RNA sample.