Transmission powder patterns of random and of highly oriented samples of natural micas have been recorded and compared with those calculated from structural data with the aid of the DIFK computer program modified to correct for preferred orientation. Intensities calculated from structural data for random and for highly oriented samples (symmetrical and oblique settings) are presented for 1M, 2M1, 2M2, 3T polytypes of muscovite, 1M, 2M1, 3T polytypes of paragonite and 1M (C2/m and C2 space groups), 2M1, 2M2, 3T polytypes of lepidolite.