Location of the intermediate abutment, length of span and number of abutments were changed in three-, four- and five-unit fixed partial dentures having two or three abutments and their influences on retentive forces of each abutment were measured after repeating load at one-point (the center) and three-points (two moreexternal points) of occluding faces of fixed partial dentures.The results were as follows:1. When repeating load was applied at the center of five-unit fixed partial dentures having three abutments, the intermediate abutment indicated the lowest retentive forces of all abutments.2. Location of the intermediate abutment between two external abutments was significant for the retentionof each abutment.3. Fixed partial dentures having two abutments became deflected in proportionally as the span between the abutments became longer. The amount of deflection was significant for the retention of each abutment.4. Five-unit fixed partial dentures having two abutments indicated the lowest retentive forces of all fixed partial dentures examined.5. Addition of one more abutment to four-unit fixed partial dentures having two abutments was not always effective in improvement of the retention of fixed partial dentures.6. Numberof loading points was significant for the retention of the fixed partial dentures.