RIP-chip is a high-throughput method to identify mRNAs that are targeted by RNA-binding proteins. The protein of interest is immunoprecipitated, and the identity and relative amount of mRNA associated with it is measured on microarrays. Even if a variety of methods is available to analyse microarray data, e.g. to detect differentially regulated genes, the additional experimental steps in RIP-chip require specialized methods. Here, we focus on two aspects of RIP-chip data: First, the efficiency of the immunoprecipitation step performed in the RIP-chip protocol varies in between different experiments introducing bias not existing in standard microarray experiments. This requires an additional normalization step to compare different samples and even technical replicates. Second, in contrast to standard differential gene expression experiments, the distribution of measurements is not normal. We exploit this fact to define a set of biologically relevant genes in a statistically meaningful way.