Abstract: An rf coil assembly for use in an NMR investigation, the assembly comprising(1) a transmitter coil (10) adapted to transmit an rf magnetic field suitable for the NMR investigation into a working region and comprising a plurality of serially connected winding elements (1-4); and(2) a receiver coil (9) electrically separate from the transmitter coil and adapted to receive an rf signal from the working region and comprising a plurality of serially connected winding elements (5-9).Winding elements of one coil are interleaved and substantially coaxial with winding elements of the other coil, and at least one of the coils comprises one or more winding elements which are counter-wound with respect to the other winding element(s) in the coil.