1. The oral absorption and the rate of loss from the body of radioactive iron were measured by whole-body monitoring in patients with functioning renal homografts. The incorporation of radioactive iron into erythrocytes was also measured.
2. The results were compared with corresponding values in normal subjects and in non-dialysed and dialysed patients with chronic renal failure.
3. The mean oral absorption and incorporation into erythrocytes of radioactive iron was intermediate between that of normal subjects and of both non-dialysed and dialysed patients with chronic renal failure.
4. The mean rate of loss from the body was not significantly different from that in normal subjects and non-dialysed patients with chronic renal failure but it was significantly less than that in dialysed patients.