RNA-FISH (fluorescence in situ hybridization) is the method of choice to quantify single mRNAs in fixed cells. Therefore, a set of approximately 48 single-labeled DNA probes complementary to the target genes are designed. After hybridization, mRNAs can be detected as single fluorescent spot using fluorescence microscopy and subsequently quantified. Using fluorescent cell cycle markers we are able to quantify mRNAs during specific cell cycle without any perturbation.