Magnetoresistance oscillations (Shubnikov-de Haas effect) and Azbel-Kaner cyclotron resonance were studied in a dilute Bi-Sb alloy (Sb concentration of 0.96 wt.%) at 4.2°K for various orientations of the magnetic field. It was found that the electron masses, and the extremal cross-sectional areas of the electron Fermi surface, decrease to approximately 80 and 62%, respectively, of the corresponding values in pure Bi. The observed changes in cyclotron masses and Shubnikov-de Haas frequencies in the alloys are consistent with the nonparabolic model and the assumption of rigid motion of the conduction band, and the valence band just beneath it, with respect to the hole band. Effective masses at the bottom of the conduction band were calculated. The electron Fermi energy and concentration in the alloy were determined. The band overlap deduced from this result is in agreement with other work. © 1964 The American Physical Society.