The contribution of theK&agr;1&agr;2asymmetry to the total observed asymmetry is calculated for x‐ray diffraction profiles from fcc specimens containing twin faults. The profiles are approximated by exp(−k2x2), (1+k2x2)−2, or (1+k2x2)−1. Calculations, using data from filed and annealed Permalloy, show that the &agr;1&agr;2asymmetry introduces no serious error in determining the twin fault probability as long as the observations are made at values of the abscissa which correspond to at least half the distance from the profile maximum to the profile zero point. For asymmetries measured closer to the profile maximum, the &agr;1&agr;2asymmetry can become important. A method to correct for the &agr;1&agr;2asymmetry is given.