Previous studies have suggested that more defects are detected on SPET than on planar DMSA images. The aim of this study was to evaluate differences between planar and SPET imaging. Sixty-four kidneys from pyelonephritic patients were studied using both techniques. An automated algorithm for reorientation and centring of the SPET images was used to minimize inter-observer variability. Reduced uptake and contour defects showed different localization on planar and SPET imaging. Coincidence of defects on both types of image was low. We also noted a dependence on defect frequency content for detectability. Image contrast played a noticeable role in the detection of defects. Differences in contrast between SPET and planar images may be responsible for the variable success in the detection of defects. Contour defects are seen more frequently on tomographic slices, whereas reduced uptake defects are seen more frequently on planar images. A difference is also noted between the cortical and calyceal zones for differently contrasted lesions. SPET and planar DMSA images can potentially provide a different diagnosis of renal lesions.