Cells from individuals with CLL who drank deuterated water (heavy water) for 6 weeks showed a turnover rate of 0.1 % to 1.1 % per day. In a second study involving CLL subjects who drank heavy water, average CLL turnover rates were in a similar range but approximately 2-fold lower than average B-cell turnover rates from healthy individuals. These studies have shown the safety and scientific value of using heavy water to study the kinetics of cell proliferation in patients and normal volunteers.