The authors studied the influence of gating, cardiac cycle, and timing of rephasing gradients upon the detection of pulmonary emboli by MRI. Serial single-section MR images were obtained in normal dogs and dogs with experimental pulmonary emboli. Images with cardiac gating, respiratory gating, and ungated images were obtained. Cardiac gating in systole and late magnetization rephasing had the best diagnostic accuracy. Gated images were clearly superior to ungated; with combined cardiac and respiratory gating, sensitivity was 82% and specificity 88%. These results are sufficiently promising to warrant further studies.