Serum titanium concentration was measured in subjects undergoing primary total hip replacement (THR) using a prospective, controlled, longitudinal study design. One group of subjects underwent “hybrid” THR utilizing a commercially pure titanium (cp Ti) acetabular component inserted without bone cement and a modular cobalt-base alloy femoral component inserted with bone cement. A second group underwent cementless primary THR utilizing a titanium-6% aluminum-4% vanadium modular femoral component and a cp Ti acetabular component. A third group of subjects consisted of contemporaneous age and sex matched controls without implants or systemic disease. Serum titanium levels are elevated at all intervals up to 3 years postoperative in patients with cementless titanium alloy THR with respect to the baseline preoperative concentration and with respect to controls without implants. The “hybrid” THRs also demonstrate serum titanium elevations with respect to controls. At this juncture, we have observed no correlation between serum titanium levels and clinical function, nor have we identified any toxic effects.