The nuclear spin-lattice relaxation time, T1, has been measured in the range of 1.1°K to 4.2°K for the metals lithium, sodium, aluminum, and copper. A combination of nuclear magnetic resonance at fixed frequency and adiabatic variation of the magnetic field was used to measure T1 as a function of field between zero and one thousand gauss. At fields of between one hundred and one thousand gauss T1 is independent of magnetic field and inversely proportional to temperature in agreement with theory. The experimental values of the relaxation time multiplied by absolute temperature in sec °K are 44±2.0 for Li7; 5.1±0.3 for Na23; 1.80±0.05 for Al27; 1.27±0.07 for Cu63. These values are in good agreement with previous experimental data at room temperature and above. At fields comparable with the nuclear magnetic dipole-dipole fields, T1 is a function of applied field. The theory of relaxation in low fields is presented in an elementary form. Qualitative agreement with theory is obtained for Al27 and Cu63; detailed agreement is obtained for Li7 and Na23. © 1959 The American Physical Society.