Vector-based methods for manipulating microRNA (miRNA) activity in vivo and in vitro face a number of disadvantages regarding biosafety, workload, and potential for therapeutic use in patients. Use of miRNA mimics and inhibitors provides an alternative for enhancing or inhibiting translational repression of target genes that could be easier applied to elucidate miRNA function. Here, we describe in detail application of miRNA mimics and inhibitors in vitro using adherent cell lines. In addition, we describe a method how they could be applied in vivo in a possible therapeutic context and provide a protocol for validation of this intervention using miRNA target protectors. We present these methods within a standard experimental design workflow that could be followed and we discuss the technical challenges that have to be taken into account.