Preliminary results of a modelling study of both steroidal and non-steroidal inhibitors of 5 alpha-reductase (5AR) are described in order to elucidate the essential structural requirements needed for the design of novel non-steroidal inhibitors. The study suggests that: (i) there is a requirement for groups to mimic the C(3) = O of the steroid substrate A-ring; (ii) the area of the active site about the C(17)-OH position of the substrate does not appear to possess hydrogen bonding groups and is unrestricted.