The configurations of eight 6- and 7-methylsulphinyl-5α-cholestanes have been determined by the pyrolytic method, and their preferred conformations were revealed by n.m.r. spectroscopy. The optical rotatory dispersions of the sulphoxides are consistent with the asymmetric perturbation of the sulphinyl chromophores by the steroid nucleus, a consequence of restricted rotation about a C–S bond. The ratio of axial to equatorial sulphoxides obtained by base-catalysed equilibration at C-7 depends upon chirality at sulphur.