The most serious controversy regarding the application of transaxial SPECT technology to 201Tl myocardial perfusion imaging is the choice between 360 degrees compared with 180 degrees data sampling techniques. The present study utilized the original 360 degrees sampled raw data of 25 patients who had both SPECT 201Tl myocardial perfusion imaging and coronary angio/ventriculography for back projection reprocessing to accomplish the 360 degrees/180 degrees comparison. The results show a high incidence, 36% (9/25), of false-positive segmental perfusion abnormality and a high incidence, 24% (6/25), of moderate to severe degree of image distortion with the 180 degrees data sampled reconstructed images. These were not observed in the 360 degrees data sampled reconstructed images. The above findings confirmed our previous preliminary conclusion that even though the 180 degrees data sampling technique has the advantage of providing improved image contrast and reduction in acquisition time it is not a reliable technique and should be abandoned. The 360 degrees data sampling is the technique of choice for transaxial SPECT 201Tl myocardial perfusion imaging.