A method and apparatus for determining the spatial distribution of the chemical shift spectra of a chosen element across a region of a body. Where the region is a slice, nuclear magnetic resonance for the element is excited preferentially i the slice. First and second pulsed magnetic gradient fields (Gx,Gy) having magnetic field gradients in first and second mutually orthogonal directions in the plane of the slice are applied. The value of the gradient of the first field is stepped through a range of first values, for each of the first values the gradient of the second field being stepped through a range of second values. The free induction decay signal after each set of one first and second field pulses is measured to form a set of free induction decay signals which is subjected to a two dimensional Fourier Transform process with respect to the first and second directions, and to an additional Fourier Transform process with respect to time to obtain chemical shift spectra for the element at each of a plurality of different locations in the slice.