We have studied band‐to‐band optical magnetoabsorption in a semiconductor quantum wire subjected to a transverse magnetic field. The magnetic field induces a blueshift in the absorption peaks and makes the linewidth narrower. Furthermore, it quenches photoluminescence and absorption in much the same way as an electric field in the quantum confined Franz–Keldysh effect (QCFKE). We call this the quantum confined Lorentz effect (QCLE), since it is the Lorentz force skewing the electron and hole wavefunctions in the quantum wire that causes the quenching. The QCLE has an advantage over the QCFKE in that it may be observed even in quantum wires with relatively leaky barriers. The other important difference is that while the QCFKE is accompanied by a redshift in the absorption or photoluminescence peak, the QCLE is accompanied by a blueshift. ©1995 American Institute of Physics.