This study measured the distortion of one-piece base metal four-unit fixed partial dentures and recorded the effect of positioning marginal reservoirs on the wax patterns. Standard wax patterns were made in a special three-piece stainless steel mold. Twenty anterior prostheses were case: 10 for the experimental group and 10 for the control group. The prostheses were case in a nickel-chromium alloy and were measured with a traveling microscope with a micrometer scale. Premarked points were designated on gingivoaxial line angles for buccolingual and mesiodistal distances and diameters to record marginal discrepancies of specimens with or without marginal reservoirs. Castings with marginal reservoirs distorded signifiantly less than did the control fixed partial dentures.