Several publications have reported a north-south asymmetry of the solar magnetic polarity in variations of the solar wind, geomagnetic activity, and polar coronal holes. The present study analyzes the polarity of the z-component of the interplanetary magnetic field (IMF Bz), finding long-term periods with a predominant polarity. IMF data was averaged using a 13-month 'boxcar' long-term averaging method that has been used to smooth the sunspot number for use in the McNish-Lincoln forecasting method. Both the averaging technique and the McNish-Lincoln forecasting method have also been used to forecast the average magnitude of Bz. However, this previous work did not examine the effect of polarity. The work reported here used the same averaging method to examine the long-term average of Bz, but also considered the polarity. The resulting averages for the period 1963--2002 showed long periods where one polarity dominated the other. Examination of the data has led us to believe this predominance is caused by a shift of the heliomagnetic equator away from the heliographic equator.