Several removable partial denture retainers were tested on a photoelastic cast of a human maxilla that had undergone a surgical resection through the midline. The conclusions based on the results of these tests are as follows. Physiologic adjustment of all the designs tested revealed a dramatic reduction in stresses when the framework were placed into position. Under load, the physiologically adjusted frameworks produced less potentially damaging stresses in the supporting structures than the unadjusted frameworks. High stresses were located at the premolar region for all the designs. Lingual retainers produced higher stress concentration than buccal retainers. In the anterior region, the I-bar retainer with a cingulum rest was the best combination for transmitting the occlusal forces along the long axis of the tooth. From the perspective of the equitability of stress transfer, the tested designs from best to worse are infrabulge I-bar retainer, either buccal or lingual retention; light wire circumferential retainer with buccal retention; and the circumferential cast buccal retention, swing-lock system.