The γ-secretase inhibitor dibenzazepine (DBZ) and the γ-secretase modulators 1 and AZ8349 were prepared as tritium-labeled compounds with high specific activity and radiochemical purity. [3H]DBZ was labeled via an iodinated precursor, [3H]1 was labeled by [3H]methylation of an O-desmethyl precursor, and [2-3H]AZ8349 was labeled via a tribromoacetyl precursor by catalytic hydrogenation. [3H]DBZ, [3H]1, and [2-3H]AZ8349 are promising in vitro imaging radioligands and have the potential to provide key information with regard to γ-secretase expression, function, stoichiometry, and pharmacology.