Thirty-seven male dialysis patients, from three university hospital centers known to have adequate iron B12, and folate stores, were entered into a controlled trial to study the effects of nandrolone decanoate (200 mg i.m. weekly) on their anemia. An initial six-month stabilization period was followed by a randomized 12-month study, with crossover between treatment and control groups occurring at six months. Patients received parenteral iron therapy plus oral folate throughout the trial. All serious illnesses or major blood losses excluded the patients from analysis. The 24 patients with remnant kidneys showed an increase in hemoglobin and hematocrit of 24% by the end of six months of treatment (P less than 0.005), with a corresponding decrement during the six months of control, but the five anephric patients showed no statistically significant change compared to those patients whose kidneys were in place during the study. Complications of treatment were minimal, with injection site hematoma the only significant local effect and a rise in triglyceride the only significant systemic disturbance. Despite the improvement in anemia, the disadvantages, including the high cost of treatment, the apparent plateauing of benefits by five months, the minimal subjective improvement in life style, the risk of i.m. injection, plus the long term effects of increased lipids, should limit this therapy to patients with remnant kidneys who have severe symptomatic anemia or frequent transfusion requirements.