A testing machine was devised and constructed for the purpose of measuring the retentive forces of maxillary complete denture bases in subjects. Forth complete denture bases were made for ten subjects with three different denture base materials, following the usual denture construction technique. Retentive forces of the forty dentures were determined at seven locations. The tests on each base were repeated three times at intervals of 5 minutes. Differences in retention values were evaluated statistically. 1) Differences in retention values were found by the differences of the denture base materials, but acrylic resin was similar to chromium cobalt alloy. 2) The chromium cobalt alloy and acrylic resin bases from master models revealed the best retention values, the gold alloy base from master model was the poor second and the acrylic resin base from snap model was the third. 3) The retention values for hook-1 revealed higher than that for hook-2 and the retention values for hook-3 revealed the lowest value.