The coefficient of true intestinal calcium absorption (a value) was measured by a double radioisotope technique in 24 patients treated by regular hemodialysis for 2–46 months. The mean a value of these patients was significantly below normal (p < 0.001). 18 of them were studied a second time after an interval of 12 months. Values at 12 months were higher than the corresponding initial values (p < 0.001). There was a trend to higher a values in the patients treated for longer periods of time. It is concluded that the defect in calcium absorption tends to reverse during the course of regular hemodialysis.