15-(ortho-123I-phenyl)-pentadecanoic acid (oPPA) in contrast to the para-isomer pPPA has a prolonged retention in the normal human myocardium. Following qualitative evaluation, a semi-quantitative analysis of oPPA-SPECT is presented in 52 patients (41 with coronary artery disease (CAD) and 11 normals). Data were compared to the results of coronary angiography (CAD patients). Up to 220 MBq 123I-labelled oPPA were injected intravenously after overnight fasting and bicycle exercise. Four minutes later SPECT acquisition (180 degrees technique) was started. In 15 patients a second dose of oPPA was injected 2.5 h later and the study was repeated under rest conditions. Compared to our qualitative analysis the semi-quantitative approach revealed a lower sensitivity of 76% for the detection of CAD (global, stenoses greater than 50%) (specificity was not analysed because the normal patients served as the control group for the calculation of normal values). Because the sensitivity does not exceed that of 201Tl-SPECT or MIBI-SPECT, oPPA is not recommended for the detection of CAD, but it may serve for the evaluation of myocardial viability in ischaemic regions.