We present a systematic study of electronic levels and recombination lifetimes for rectangular and V-shaped quantum wires (QWRs) in a magnetic field B. In both cases, the effect of B is a modification of the subband dispersion consisting mainly in a flattening at small values of the wave vector: this feature is explained with the appearance of Landau levels inside the wire profile, and it becomes more pronounced with growing magnetic field. As a consequence, an increase in the calculated free-carrier lifetime with the field strength is found. This behaviour is experimentally observed in InxGa1—xAs/GaAs V-shaped quantum wires with an In content x = 0.10, where the exciton is ionised and the recombination mechanism is supposed to be a free-carrier one; a quantitative agreement between theory and experiment is found.