Intense field ionisation mass spectra have been obtained with an A.E.I. M.S.7 mass spectrometer, used with very simple modifications to the ion source. Some features of the spectra of a variety of compounds are given and the spectrum of acetone is discussed in detail. A special feature of this spectrum is the variety of ions with a mass greater than that of a single molecule. The relatively small energy spread of the field ion source enabled resolving powers, higher than those possible with a spark source, to be obtained. Multiplets occurring in the spectra were easily resolved.