Seven Ti-6Al-4V femoral prostheses were compared with a conventional Charnley type of a cobalt-based alloy. Structural stiffness criteria for anteroposterior, mediolateral, and torsional loadings were considered and compared. The stems were replicated and sectioned at 10-mm increments, the cross-sectional outlines were digitized, and the stiffness criteria were calculated. Although Ti-6Al-4V was the more flexible alloy, some titanium alloy prostheses were stiffer than the Charnley type—up to approximately 70 percent greater in bending and 20 percent in torsion. In contrast, other titanium alloy stems had only 30 to 90 percent of the Charnley stiffness criteria. These data for the first time provide a simple means for the orthopedic surgeon to determine whether his stem of choice is comparable to the well-established Charnley hip or whether, depending on his perception, he wants a stiffer or more flexible one.