The bone mineral content (BMC) and bone mineral density (BMD) of the femoral midshaft from 15 skeletally mature male rats were measured by Single Photon Absorptiometry (SPA), and comparisons made to fracture strength of the femoral diaphysis and the femoral neck. In stepwise regression the factors contributing significantly to the ultimate bending moment of the shaft were BMC and femoral length. BMC correlated strongly with the ultimate bending moment of the femoral diaphysis (r2 = 0.63, P < 0.01). The correlation between BMC and ultimate moment of the femoral neck was moderate (r2 = 0.51, P < 0.01). The correlations between BMD and mechanical parameters were lower than the corresponding values for BMC, with a significant result only for the bending moment of the femoral diaphysis (r2 = 0.48, P < 0.01). In conclusion, BMC rather than BMD, is most predictive for fracture strength of the femur in rats.