As a guide to the development of new and more selective inhibitors of phenylethanolamine N-methyltransferase (PNMT) vs the alpha2-adrenoceptor, we have performed a comparative molecular field analysis (CoMFA) on a series of 80 benzylamine analogues. Using the models obtained, we have proposed a series of 3-trifluoromethyl-1,2,3,4-tetrahydroisoquinolines and predicted the activity of other analogues.