The stereo-array isotope labeling (SAIL) method 1) has been successfully applied to determine the structures of relatively large proteins, which are difficult to assess by conventional NMR approaches. These applications require protein samples exclusively composed of SAIL amino acids, and the samples are prepared primarily by cell-free protein expression systems. This might impose a further barrier for promoting the SAIL method in the NMR community. However, for the various other applications of SAIL amino acids to address the local conformations and dynamics of selected amino acid types, in many cases the standard cellular protein expression systems can be used to prepare the NMR samples. Therefore, we have been focusing on the development of new possibilities for using selectively SAIL proteins to study the dynamics of proteins and protein complexes. 2-4) In this presentation, we will describe some of our latest results on the applications of selectively SAIL proteins for studying various side-chain dynamics, including aromatic ring flipping, proton exchange rates of the side-chain hydroxyl, sulfhydryl, and amino groups, and disulfide bond isomerization. We are also attempting to apply the selective SAIL method to very large systems. Some perspectives on these latest developments will be discussed, based on recent results.