Aromatase is a cytochrome P450 isozyme, whose inhibition is known to be therapeutically relevant in the treatment of the breast cancer. A comparative molecular field analysis (CoMFA) has been carried out on a series of non-steroidal aromatase inhibitors belonging to two different structural classes. One subset of compounds consists of fadrozole analogues and was studied in a previous work, from which a 'local' 3-D quantitative structure-activity relationship (QSAR) model for the inhibition of aromatase was obtained. In the present paper, that model is extended to include a second subset of compounds bearing a tetralone nucleus and acting at the same enzyme site with the same mechanism as the azoles. The critical alignment step has been solved by using two different steroidal inhibitors of aromatase as rigid templates, on which the non-steroidal compounds have been superimposed. The final 3-D QSAR models are discussed in terms of predictivity and some implications regarding the steric and electronic requirements of steroidal and non-steroidal inhibitors are pointed out.