The native intracellular environment of proteins is crowded with metabolites and macromolecules. However, most biophysical information concerning proteins is acquired in dilute solution. To determine whether there are differences in dynamics, nuclear magnetic resonance spectroscopy can be used to measure 15N relaxation in uniformly 15N-enriched apocytochrome b5 inside living Escherichia coli and in dilute solution. Such data can then be used to compare the fast backbone dynamics of the partially folded protein in cells to its dynamics in dilute solution by using Lipari-Szabo analysis. It appears that the intracellular environment does not alter the protein's structure, or significantly change its fast dynamics. Specifically, the cytosol does not change the amplitude of fast backbone motions, but does increase the average timescale of these motions, most likely due to the increase in viscosity of the cytosol.