A prospective comparison of conventional scintigrams and single-photon emission computed tomography (SPECT) studies of the liver and spleen was carried out. Care was taken to insure high-quality, artifact-free studies. Two hundred patients were imaged by both methods. A definitive diagnosis of normal was established in 86 cases, abnormal in 107 cases, and seven cases were indeterminate. All studies were read by two observers and graded as to degree and type of abnormality seen. ROC curves were constructed and errors of interpretation studied to identify problems. One observer showed no difference in performance between the two methods. The other showed a small improvement with SPECT. Image artifacts apparently contributed to errors of interpretation in 24 of 54 cases using SPECT. SPECT appears comparable with conventional scintigraphy and may improve specificity. Improvements are needed in SPECT imaging equipment and image display capability to realize fully the potential of SPECT.