When a pinhole collimator is to be used for tomographic studies the standard SPECT software has to be modified so as to avoid serious image distortion outside the axis of rotation. The MTF measured at the axis of rotation shows that the better resolution of the pinhole collimator as compared with that of a parallel-hole collimator improves the tomographic image. The low sensitivity of the pinhole collimator excludes the use of an aperture smaller than 6 mm for patient tomographic studies where the activity which may be administered is restricted.