For helium II in uniform rotation, the component of mutual friction along the rotational axisBzhas been studied. The attenuation of second sound transverse to the axis of rotation (characterized by the parameterB) has been compared with the attenuation in the direction of the axis (measured byBz). It is shown: thatB/Bz> 500 over a large range of temperature and frequency; thatBzis not very reproducible; thatBzis dependent on the second sound amplitude; and thatBzis not linear in &OHgr;, the rate of rotation. Within the temperature and frequency range covered by Hall and Vinen the present data onBagree with the results of these authors. Near the &lgr; point,Bincreases rapidly. The anomalous dependence ofBon &OHgr; near 2.0°K as reported by Hall and Vinen is not observed. Some preliminary measurements of the parameterB′ are mentioned.