A series of fluorinated pyridazinone derivatives with IC50 values ranging from 8 to 4000 nM for the mitochondrial complex 1 (MC1) have been prepared. Structure-activityrelationship (SAR) assessment indicated preference of the fluorine label to be incorporated on an alkyl side chain rather than directly on the pyridazinone moiety. Tissue distribution studies of a series of analogues ([18F] 22-28) in