A method for producing a hyperpolarised sample material for use in NMR, comprises providing in a cryogenic region a target material containing a first hyperpolarisable nuclear species, a second hyperpolarisable nuclear species, and a nuclear spin polarising agent. Microwave energy is supplied to the cryogenic region to excite electron spin transitions in the polarising agent in the presence of a magnetic field. The first hyperpolarisable nuclear species is thereby caused to interact with the electron spin system in the polarising agent and generate hyperpolarisation of the said first nuclear species of the target material. The target material is then subjected to a lowered magnetic field, wherein the lowered magnetic field facilitates polarisation transfer by nuclear thermal mixing between the species, and thereby hyperpolarise the second nuclear species. Advantageously, the method makes use of an apparatus containing two magnets (2,6) producing opposed magnetic fields, to produce a small mixing magnetic field between the magnets.
