By replacing the alkyl chain in a metomidate ester with 18 F]fluorination reactions using conventional and microwave heating. Organ distribution, frozen section autoradiography and metabolite analysis were performed. The decay-corrected radiochemical yields of 1 and 2 were 2678 and 2378%, respectively, when they were prepared using conventional heating. By performing microwave heating, the reaction time could be decreased and the yields of analogues 1 and 2 could be increased to 57712 and 51718%, respectively. Organ distribution studies in the rat showed considerable uptake in the lungs, adrenals and liver. Both compounds bound with low nonspecific binding (1: approx. 20-30%; 2: 2.9% or lower) to tissue from pig and human normal and pathologic adrenals. Metabolite analyses were performed in rats after 5 and 30 min for tracer 1 (2076 and 271%) and tracer 2 (2775 and 674%). Both compounds are interesting candidates for the detection of different types of adrenal disorders.