  We show that spin-flip rotation in a semiconductor quantum wire, caused by
the Rashba and the Dresselhaus interactions (both of arbitrary strengths), can
be suppressed by dint of an in-plane magnetic field. We found a new type of
symmetry, which arises at a particular set of intensity and orientation of the
magnetic field and explains this suppression. Based on our findings, we propose
a transport experiment to measure the strengths of the Rashba and the
Dresselhaus interactions.
