Abstract: Radio-iodine-labelled omega-phenyl fatty acid of the formula: ##STR1## in which: X is an alkylene group having from 6 to 20 carbon atoms; R is hydrogen or an alkyl or alkoxy group having 1 or 2 carbon atoms; Y is hydrogen, an alkali metal ion, alkaline earth metal ion or ammonium ion; and I is a radioactive iodine-123 or iodine-131 isotope which may be in the ortho- or para-position of the benzene nucleus,a process for the preparation of these radio-iodine-labelled phenyl fatty acids, and products containing them for scintigraphic examination of various organs of the body such as the heart and the liver.