The conversion of a 40 Mc/s Varian nuclear magnetic resonance spectrometer to 80 Mc/s operation is described. The increase in maximum field strength from 12 to 22.5 kG was achieved by the use of conical Permendur pole caps. The factors affecting pole-cap geometry are discussed. Sufficient field homogeneity for the production of high resolution 80 Mc/s hydrogen nuclear magnetic resonance spectra was achieved with Golay electric shim coils. Further stability of the magnetic field, enabling spectra to be recorded on precalibrated chart paper, was achieved by a double audio-frequency modulation technique. Notes are also given on the associated changes required to the electronic circuits.