The effect of three heat treatments on plane-strain fracture toughness (K _Ic), fatigue crack growth rate (da/dN), and tensile behavior of a commercial powder metal alloy, CPM 10V, was investigated. Fracture toughness was increased by increasing the tempering temperatures and decreased by increasing the austenitizing temperature. These changes were related to changes in yield strength and the resulting crack tip plastic zone sizes. Fracture toughness resulting from any of the three heat treatments was inversely related to the hardness. Fatigue crack growth followed the Paris Law for some portion of the curve and crack growth exponents, n, were virtually unchanged by the heat treatment. The linear portion of the growth curve was shifted to higher stress intensity ranges for heat treatments yielding higher fracture toughness. Fatigue crack growth behavior in the high growth region was determined mainly by the fracture toughness of the specific heat treatment. / M.S.