Seismic refraction measurements were carried out in 1970--1971 near Byrd Station, Antarctica, with a specific emphasis on the determination of seismic wave attenuation. The primary difficulty in interpreting field results is the extreme sensitivity of the observed attenuation to small variations in the seismic velocity gradient and its first derivative. Detailed velocity analysis, based on multiple surface-reflected arrivals, has made possible an estimate of the average internal friction for compressional waves between 100- and 500-m depth (temperature, -28¿C): Qp-1=0.0014 at 136 Hz, with upper and lower standard error estimates of +0.0005 and -0.0008, respectively. This value has been compared with laboratory measurements by Kuroiwa (1964) on cold slightly impure polycrystalline ice. The comparison required extrapolation of Kuroiwa's results to lower frequency, a correction for the difference shear and compressional wave absorption, and an estimate of the amount of salt contained in ice frozen from a known solution. The agreeement between field and laboratory results is good for the ionic impurity concentration measured in the ice near Byrd Station. All field measurements of Qp-1 by reflection shooting in Antarctica and Greenland, although they cannot be assigned to a particular temperature, are also in satisfactory agreement, as are some previous determinations by refraction shooting in Greenland, although some from the high interior part of the Greenland ice sheet are seriously discrepant, probably because of inadequate knowledge of the seismic velocity gradient. We conclude that with the possible (but unlikely) exception of the central Greenland ice sheet, cold polar ice sheets exhibit an internal friction in the frequency range 50--200 Hz that is completely explained by the two fundamental mechanism in polycrystalline ice: molecular relaxation (dominant at relatively cold temperatures) and grain boundary viscosity (dominant near the melting point). There is no evidence of any additional mechanism associated with internal structures such as bubbles or microcracks.