Fatigue tests to failure of compact bovine bone specimens were conducted at five stress amplitudes (65–108 MN/m²) and four temperature levels (21–45°C). The resulting relationships between fatigue life and stress amplitude, bone temperature, and bone density have been reported (Carter and Hayes, 1975). In the present study, the bone specimens were categorized into four microstructure groups based on the extent of secondary Harversian remodeling. A significant correlation (P < 0.001) between density and microstructure group was shown with primary bone specimens generally being more dense than secondary Haversian specimens. A positive correlation (P < 0.01) between fatigue life and density was revealed within each structural group. In addition, a negative correlation (P < 0.001) between fatigue life and the extent of Haversian remodeling was shown even after appropriate adjustments for density differences. These data suggest that Haversian remodeling of primary bovine bone reduces fatigue resistance not only by decreasing bone density, but also by creating an inherently weaker structure.