5-Ethynyl-UTP (5-EUTP) can be incorporated into RNA using standard nucleotide mixtures and T7 RNA polymerase in vitro transcription. For a partial modified RNA we recommend to replace the natural base by only 1-10%. Modified mRNA is ready for labeling with marker azides (e.g. fluorescent dyes for tracking and imaging or cross-linking to other biomolecules) by click chemistry.