New high signal-to-noise ratio 21 cm HI line profiles have been obtained for 104 galaxies with the Green Bank 43 m telescope. The primary sample is composed of isolated spirals with no companions within one degree radius and a median ratio of optical diameter to beamwidth of 0.17. An effort was made to insure linearity of baseline fitting and precise flux calibration to better than five percent. Two quantitative measures of asymmetry are applied to assess the occurrence of lopsidedness in the global HI profiles. In agreement with previous estimates, one half of the galaxies show significant HI profile asymmetries. The lopsidedness cannot be explained by pointing offsets, but rather, must result from non-circular motions, confusion with unidentified companions within the telescope beam or true distortions in the HI distribution.
ADS abstract