Fracture toughness parameters were determined for V-notched specimens cut from adult bovine femora tested in three-point bending at strain rates ranging from 7 × 10⁻⁶ to 3 × 10⁻² sec⁻². The average critical crack length is 0.36 mm and the plastic zone size is 17 μm, corresponding to a few lamellar thicknesses. The critical stress intensity factor K_IC averaged 5.7 MPA m^1/2 and was found to be independent of the existence of a pre-crack. There is a weak, but positive, correlation between K_IC and strain rate expressible as K_IC = 0.70logε + 8.2 ± 1.2MPA m^1/2.