Room-temperature free-carrier Faraday rotation measurements in the wavelength range 6–25 μ and Hall-coefficient measurements have been made on polycrystalline n-type samples of InAsxSb1−x alloys of carrier concentration ~1017/cm3. Using these data and a Kane equation for the conduction band, values of the bottom of the band effective mass m0* have been determined over the whole alloy range. The results are compared with similar data from magnetothermoelectric power measurements and also with previously calculated data. From the m0* results, values of the square of the matrix element P2 have been calculated as a function of x.