X-ray crystallography and NMR spectroscopy are complementary techniques for structure determination, but each method has its drawbacks.

X-ray:
- crystal needed
- crystallization artifacts
- unphysiological environment
- low temperature
- no time resolution
- no hydrogens seen

NMR:
- limited molecular size (50 kDa)
- highly concentrated sample solutions (mg quantities of protein needed)
- only local structure information (short range distance restraints)
- relatively poor sensitivity
- no R-factor