We demonstrate 1 H amide resonance line widths <300Hz in 1 H/ 15 N heteronuclear correlation (HETCOR) spectra of membrane proteins in aligned phospholipid bilayers. This represents a substantial improvement over typically observed line widths of ∼1kHz. Furthermore, in a proton detected local field (PDLF) version of the experiment that measures heteronuclear dipolar couplings, line widths <130Hz are observed. This dramatic line narrowing of 1 H amide resonances enables many more individual signals to be resolved and assigned from uniformly 15 N labeled membrane proteins in phospholipid bilayers under physiological conditions of temperature and pH. Finding that the decrease in line widths occurs only for membrane proteins that undergo fast rotational diffusion around the bilayer normal, but not immobile molecules, such as peptide single crystals, identifies a potential new direction for pulse sequence development that includes overall molecular dynamics in their design.