The 3D HN(CA)NNH experiment is a triple-resonance experiment specifically designed to provide sequential asignment between the amide NH proton of one residue and the amide nitrogens of the preceding and the following residues via the intervening ¹³CA spin by means of the  ¹J(NH) and ^1,2J(N,CA) coupling constants.

Implementation on AVANCE spectrometers equipped with a third channel. Improved versions using pulsed field gradients (PFGs) are also available and, therefore, in such cases gradient technology is required.

The experiment is applied on ¹⁵N,¹³C-labeled proteins. Because the amide (NH) protons are involved, the HNCO experiment must be recorded in H₂O.

The original 3D HN(CA)NNH pulse sequence ( 93JB113 ) consisted of the following steps:

1. Initial transfer from ¹H to ¹⁵N via ¹J(NH) using an INEPT pulse sequence.
2. ¹⁵N chemical shift evolution during a variable t₁ period followed by a period to achieve antiphase ¹⁵N magnetization with respect to ¹³CA  spins.
3. Magnetization transfer to ¹³CA by simultaneous 90º ¹⁵N and ¹³CA pulses.
4. The active antiphase ¹³CA magnetization is allowed to refocus during another fixed delay. On the other hand, a new antiphase ¹³CA magnetization with respect of the following or preceding ¹⁵N amide residue is created.
5. Magnetization transfer to ¹⁵N is achieved by simultaneous 90º ¹⁵N and ¹³CA pulses and a period is inserted to refocus ¹⁵N-¹³CA coupling.
6. ¹⁵N chemical shift evolution during variable t₂ period.
7. Magnetization is transferred back to the NH protons by a retro-INEPT pulse train.
8. Proton acquisition under ¹⁵N decoupling.

Several improved versions have been proposed incorporating the following modifications:

• 2H-decoupling for deuterated proteins
• Two related HNN and HN(C)N experiments have been reported incorporating selective decoupling, gradient coherence selection, constant time periods and PEP methodology. ( 01JB135-20 )
• Exclusive correlation to the following residues can be achieved from a 3D (H)N(COCA)NH ( 95JB323 ) and 97JB94 ) and from a 4D HN(COCA)NH ( 93JACS4369 , 96JMRB194-111 , and 95JB323 ) experiments.
• A closely related 3D H(NCA)NNH experiment is proposed to correlate amide nitrogen of one residue and the amide protons of the preceding and the following residues via the intervening ¹³CA spin ( 93JB113 ). Correlation of amide proton and nitrogen resonances belonging to continuous residues can also be extracted from a  single 4D HN(CA)NH experiment ( 97JMR214-124 ).
• A 3D HN(CA)N experiment has been reported to correlate backbone 1H and 15N chemical shifts of an amino acid residue with the 15N chemical shifts of both the sequentially preceding and following residues. The experiment is highly suitable for the assignment of proline resonances ( 00JB337-18 )

The 3D HN(CA)NNH experiment can be recorded in automation mode. More details on practical implementation of the 3D HN(CA)NNH  experiment on AVANCE spectrometers can be found in the corresponding Tutorial 3D HN(CA)NNH experiment

The HN(CA)NNH  experiment affords a 3D spectrum in which ¹H, ¹⁵N and ¹⁵N chemical shifts are displayed in three independent dimensions. Three different connectivites can be observed:

• ¹⁵N(i) - ¹⁵N(i) - ¹⁵N(i) due to the  ¹J(NH) +  ¹J(N(i),CA(i)) +  ¹J(N(i),CA(i)) mechanism.
• ¹⁵N(i) - ¹⁵N(i-1) - ¹⁵N(i-1) due to the  ¹J(NH) +  ¹J(N(i),CA(i)) +  ²J(N(i-1),CA(i)) mechanism.
• ¹⁵N(i) - ¹⁵N(i+1) - ¹⁵N(i+1) due to the  ¹J(NH) +  ²J(N(i),CA(i+1)) +  ¹J(N(i+1),CA(i+1)) mechanism.

See list of 3D triple-resonance NMR experiments for doubly-labeled proteins.