Three hundred and eighty-one consecutive patients referred to our Nuclear Medicine Service from the Cardiology Department during a period of two years have been studied to evaluate Coronary Artery Disease (CAP) using 99mTc-MIBI single photon emission computed tomography (SPECT). The sensitivity and specificity for detecting CAD in the whole group of patients, referred (n = 161) or not (n = 220) for coronary angiography, were calculated following Diamond's method, and were found to be 87% and 92%, respectively. Diamond's method estimates these values from those obtained in the subset of patients with angiography referral (sensitivity 91% and specificity 85%) and the pattern of SPECT responses of both groups (69% and 52%, respectively). A new segmental score system was used to evaluate the location and extent of CAD in the catheterized group. The sensitivity for detecting individual artery disease was 69% and specificity was 81%. The sensitivity in patients with single, double and triple-vessel disease was 90%, 96% and 89%, respectively. In the subgroup of patients without infarction (n = 66) the sensitivity and specificity were 76% (19/25) and 90% (37/41).