1. 51Cr red cell mass (RCM), 51Cr red cell survival (RCS) and plasma parathyroid hormone (PTH) levels were measured in 27 stable chronic haemodialysis patients with a variable degree of clinical secondary hyperparathyroidism. Included were five patients who had had total parathyroidectomy.
2. The results showed a strong negative correlation between PTH and RCS (r = −0.67, P<0.001) and a positive correlation between RCS and RCM (r = + 0.53, P<0.005). However, the negative correlation between PTH and RCM was weak (r = −0.45, P<0.02). When the 13 patients with normal PTH levels (mean 0.18 ± 0.12 μg/l) were compared with the 14 patients with raised levels (mean 1.35 ± 0.71 μg/l), there was a marked difference in RCS (P<0.005) but no difference in RCM.