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A multicompany research effort was initiated to develop characteristic properties of a powder metal steel relevant to fatigue design of structural components. A low-alloy steel with the composition 0.85 % molybdenum, 0.5 % carbon was tested in the quench hardened and tempered condition. Density effects were examined utilizing 7.0 g/cm3 and 7.4 g/cm3 material, and porosity size and shape effects were examined by varying the sintering temperature of the 7.4 g/cm3 material to promote pore rounding. Results indicate that increasing the density increased both the monotonic and fatigue properties. Increasing the sintering temperature to promote pore rounding further improved the fatigue performance at low strain amplitudes. However, at high strain amplitudes the beneficial effects of pore rounding were not realized due to the dominant effects of surface carburization.