A test program has been conducted to determine the influence of geometrical variables on the ability of the notch bend and single-edge-notch tensile tests to measure valid plane strain fracture toughness value. Data were obtained on 2024-T851 aluminum, D6AC steel heat treated to yield strength values of 208 and 247 ksi, and 6A1-4V titanium. The results indicated that in the bend test four-point loading produced more reproducible values than three-point loading. Fracture toughness values were valid when the major span length-to-width ratio was equal to or greater than four and the crack length-to-width ratio was between 0.20 and 0.40. The single-edge-notch produced less variability than the notch bend test and in general, the point at which the onset of slow crack growth occurred was more easily defined. Valid fracture toughness values were obtained using the existing calibration curves in specimens where the crack length-to-specimen width ratio was between 0.20 and 0.40. (Author).