Effects of coherences between the nuclear spin eigen-states on the non-thermal nuclear polarization spectra in field-cycling experiments are described. It is shown that coherences are efficiently formed at magnetic fields where the nuclear spin levels exhibit anti-crossings and can be transferred to the NMR observables by non-adiabatic field variation. Time evolution of the coherences results in oscillating contributions to the NMR signal intensities. The effects as demonstrated here with the example of photo-chemically generated nuclear polarization of N-acetyl tryptophan are of general nature and therefore have implications for other experiments with hyperpolarized systems that employ field variation. (c) 2006 Elsevier B.V. All rights reserved.