Pseudocontact shift (PCS) contains rich structural information of proteins in structural and chemical biology. 19F-PCS is determined in live mammalian cells via dual labelling of the target protein with a paramagnetic tag and a 19F-tag, which is achieved by varied reactivity of solvent exposed cysteines in selection of different types of tags. About 0.1 ppm 19F-PCS can be observed over 20 Å from the paramagnetic center in the live cells.