The first proposals for n.m r. scanning in medical diagnosis were made by Damadian (1971
a
; 1972) and were followed by Lauterbur (1973). Damadian’s method of scanning used the principle that the forced precessions of a nuclear magnetization under radio frequency (r.f.) driving field specify the conditions for obtaining spatial resolution of the signal producing domains of a nuclear resonance sample. Sufficient coupling of the nuclear spins to the radiation field to produce a signal detectable by r.f. spectroscopy requires that the stringent Bohr frequency condition,
hv = µH
0
/I
, be met. It became possible to construct, with the aid of direct current auxiliary coils, a small volume, called the resonance aperture, inside the applied static field of the magnetic resonance experiment. The correct value of H
0
for the applied frequency is restricted to this aperture. The technique (Damadian 1972) was developed to provide a method for non-surgically detecting chemical abnormalities in the diseased organs of patients (Damadian 1971
a
). The first n.m.r. scans of normal patients and of those with malignant disease are discussed.