The use of 123I-N,N,N'trimethyl-N'-2-hydroxy-3-methyl-5-iodobenzyl-1,3-propanediami ne (123I-HIPDM) as a lung perfusion tracer in a patient with pulmonary embolism is shown. 123I-HIPDM is compared with 99mTc-labeled human albumin microspheres (HAM) using both planar and tomographic (SPECT) imaging. Pulmonary segmental defects are shown by 123I-HIPDM as well as by HAM, with a slightly better definition of perfused areas. Tomograms better show segmental shape of perfusion defects. 123I-HIPDM may be proposed as lung perfusion tracer for both clinical and experimental purposes.