A new synthetic pathway for the preparation of no-carrier-added (n.c.a.) [ 7 3 , 7 5 Se]selenoethers was investigated in order to enlarge the scope of available radioselenated compounds. Starting from n.c.a. 7 3 , 7 5 Se 0 , an isonitrile and an amine, the preparation of appropriate disubstituted radioselenoureas via homogenous and polymer-supported reactions was examined. Alkylation of these intermediates yielded the corresponding [ 7 3 , 7 5 Se]selenouronium salts. Hydrolysis under basic conditions provided the [ 7 3 , 7 5 Se]alkylselenolates and a subsequent alkylation yielded various asymmetric [ 7 3 , 7 5 Se]selenoethers with radiochemical yields of 13-56% within a reaction time of 130min in the homogenous phase and 35min using the polymer-supported synthesis.