An important component of the stress response, as well as many other biological systems, is the change in relative concentration of specific mRNAs following induction (1). Conventional techniques of differential screening may be sufficient for the detection and identification of some of these differentially expressed mRNAs, especially those of relatively high abundance. However, mRNAs displaying more subtle changes in their expression may be difficult to detect. This is particularly true for rare mRNAs showing relatively modest differences (10-fold or less) or for mRNAs expressed within only a subpopulation of cells in a sample.