A series of prazosin analogues comprised of N-acyl derivatives of N'-(4-amino-6, 7- dimethoxyquinazolin-2-yl) piperazine was prepared and the nature of their binding to a,- adrenoceptors was investigated. Derivatives with a,@-unsaturated acyclic acyls had some affinity but no irreversible action at the receptor. Other potent compounds, also without irreversible activity, contained cinnamoyl or (pheny1amino) thiocarbonyl residues. High ...