Apparatus is provided for causing nuclear magnetic resonance in a plurality of samples. The apparatus comprises a magnetic system for generating a magnetic field including a working volume in which the magnetic field is substantially homogeneous. A sample holder is adapted to hold the plurality of samples within the working volume. A common transmitting means provides radio frequency signals simultaneously to each of the samples thereby causing nuclear magnetic resonance within them. A multiple receiver array detects the nuclear magnetic resonance signals using a plurality of receiving means in corresponding receiving circuits where each circuit has a different spatial sensitivity to each sample. A probe and sample holder according to the invention are also provided.