This invention relates to triiodized dicarboxylic acid anilides containing radioactive iodine of the formula ##SPC1##WhereinR.sub.1 is hydrogen, carboxyl, N-acylamino, N-acylaminomethyl, N-alkyl-N-acylamino, N-butyrolactamyl, or an ##EQU1## group, wherein R.sub.3 and R.sub.4 are each hydrogen, lower alkyl or hydroxyalkyl, or R.sub.3 and R.sub.4 together with the nitrogen atom form a 5 to 7 member heterocyclic ring which can contain a further oxygen, nitrogen or sulfur hetero atom;R.sub.2 is hydrogen, lower alkyl or hydroxyalkyl; andX is straight-chain or branched alkylene of 1-14 carbon atoms, which can be interrupted by one or more oxygen or sulfur atoms,As well as the physiologically acceptable salts thereof with suitable bases. These compounds are especially useful in the preparation of radioactive functional diagnostic agents.