The 4D HNCOCA experiment has been designed to trace out backbone connectivites in large proteins and protein complexes.

Sucessful implementation on AVANCE spectrometers equipped with a triple-resonance probehead equipped with PFGs. The experiment is recorded on a ¹³C,¹⁵N-labeled protein in H₂O.

The 4D HNCACO sequence was described in 99JACS2571 and it is a simple extension of the 3D HN(CA)CO experiment. It uses the TROSY principle. A closely related 4D HNCO(i-1)CA(i) has also been proposed ( 99JB309-15 ).