The analysis of the structure, topology, and dynamics of membrane polypeptides provides important clues for the understanding of their functional mechanisms. The interactions of these peptides and proteins are often characterized by a high degree of mobility, and solid-state NMR spectroscopy is a method that allows the monitoring not only of the structure but also of the dynamics of membrane polypeptides. Previously, it has been demonstrated that the N-15 chemical shift obtained from uniaxially oriented samples directly correlates with the alignment of the NH vector relative to the magnetic field direction and therefore also the tilt angle of helical polypeptides. Theoretical considerations indicate that under conditions of fast diffusion around the membrane normal the proton-decoupled N-15 spectrum obtained from polypeptides associated with non-oriented membranes should also be a good indicator of the helix tilt angle. Here we provide experimental proof of this novel concept and discuss its advantages and limitations. The approach opens up new avenues to investigate the interactions and dynamics of membrane-associated polypeptides, as it allows one to vary the environmental conditions in a manner not possible with oriented samples.