We have measured the thermal-neutron spectrum throughout the unit cell of several D 20-moderated natural-uranium lattices using both differential and integral methods. For the differential measurements the neutron diffraction method was used, and for the integral measurements, space-dependent spectra were deduced from activation of gold and lutetium detectors. To obviate the numerous corrections normally required for the diffraction method, the total efficiency of the crystal spectrometer was determined using a beam with a known spectrum from a D2O thermal column. Satisfactory agreement was found between the activation measurements and theoretical results obtained with the THERMOS Code. However, effective neutron temperature changes derived from the differential spectra were systematically lower than the THERMOS calculations. Some uncertainty remains as to the precision of the differential spectra due to the method of calibration and the perturbing effect of the beam tube. Nevertheless, most of the measured spectra are in reasonably good agreement with calculated spectra.