Sequence elements within mRNA-untranslated regions and their binding partners are key controllers of mRNA stability. Changes in mRNA stability can often be detected by changes in steady-state mRNA abundance, or a more careful analysis of mRNA half-lives can be performed following transcriptional repression. This chapter presents methods to isolate RNA from both yeast and mammalian cells for either steady-state or half-life analyses. In addition, two reliable methods to quantitate mRNA levels, northern blot analysis and real-time PCR, are outlined and compared.