The present invention relates to methods for the preparation of chemically aminoacylated tRNAs for the purpose of introduction of markers into nascent proteins. The present invention also relates to methods for the non-radioactive labeling, detection, quantitation and isolation of nascent proteins translated in a cellular or cell-free translation system utilizing chemically aminoacylated tRNAs. tRNA molecules are misaminoacylated with non-radioactive markers which may be non-native amino acids, amino acid analogs or derivatives. Markers may comprise cleavable moieties, detectable labels, reporter properties wherein markers incorporated into protein can be distinguished from unincorporated markers, or coupling agents which facilitate the detection and isolation of nascent protein from other components of the translation system.