INTRODUCTIONBacteria growing in biofilms often express a different subset of genes compared to the same strains growing planktonically. Quantitative reverse transcriptase real time PCR (qRT-PCR) can be used effectively to quantify the number of RNA transcripts of specific genes from bacteria growing in biofilms. qRT-PCR has a large dynamic range and may be used to verify gene expression data obtained from microarrays. In addition, qRT-PCR is sensitive, and therefore may be used to quantify gene expression from biofilm samples where only a small amount of biological material is available, as in samples obtained by laser capture microdissection microscopy (LCMM). The most commonly used qRT-PCR methods are the SYBR Green and dual-labeled probe (Taqman) approaches. Both approaches use reverse transcription to convert mRNA to cDNA, followed by PCR amplification of the cDNA. This article describes steps involved in aspects of qRT-PCR including (1) primer design, (2) primer and probe performance testing, (3) qRT-PCR using the Corbett Rotor-Gene system, and (4) data export and analysis.