RNA-binding proteins play important roles in all aspects of RNA metabolism, particularly in the regulation of mRNAs and subsequent control of gene expression. RNA Immunoprecipitation (RIP), much like Chromatin Immunoprecipitation (ChIP), is a method for analyzing the interactions between proteins and nucleic acids. In the June issue of Cold Spring Harbor Protocols, Jesper Svejstrup and colleagues from the London Research Institute provide RNA Immunoprecipitation to Determine RNA-Protein Associations In Vivo, a detailed set of instructions for RIP analysis. Proteins and RNAs are cross-linked by formaldehyde treatment and immunoprecipitated. RNAs are then recovered and characterized by RT-PCR. The method is particularly useful for kinetic analysis of interactions at different timepoints and under different environmental conditions.