We report a search, at wavelengths between 402 and (850 \mathrm{~nm}), for anomalies in the Venus polarization curve near the (22^{\circ}) halo scattering angle for ice crystals (phase angle (158^{\circ}) ). Such anomalies, if present, can be interpreted as due to halo birefringence peaks. Anomalous polarization was indeed found in the scattering angle range (23-25^{\circ}), at wavelengths of (622 \mathrm{~nm}) and longer. The largest anomaly was about (0.4 %) in degree of polarization and occurred at the longest wavelength. The width of the anomaly was (1-3^{\circ}) in scattering angle; both magnitude and width varied with time. Mostly, the anomaly consisted of a dip in polarization (as expected), but one run shows a peak at 622 and (712 \mathrm{~nm}). One explanation of the dip is halo scattering by (\mathrm{H}{2} \mathrm{SO}{4})-contaminated ice crystals located in the upper haze layer, but the observed deep red color of the anomaly does raise doubts about this mechanism or its completeness. Rapid fluctuations are superposed on the dip; they may be explained by transparency fluctuations due to moving atmospheric features at higher levels. The anomalous peak at 622 and (712 \mathrm{~nm}) requires a separate explanation; it might be due to a transient polarized feature in the upper atmosphere, either overcompensating or obscuring the dip. The physical nature of this feature could not be identified. To separate transient time-dependent effects from scattering-angle effects and to develop polarimetry into an effective remote-sensing tool for birefringent atmospheric constituents, a high-spatial-resolution (spectro-)polarimeter is required, operating from an orbiter. We advocate equipping planetary orbiters with such polarimeters. 1993 Academic Press, Inc.