The effects of intramuscular 200-mg nortestosterone decanoate (ND) on red cell 2,3 diphosphoglycerate (DPG) concentration and packed cell volumes (PCV) were compared in 9 patients undergoing chronic hemodialysis for renal failure and in 18 control patients undergoing hemodialysis but not receiving ND. Subjects had received the drug 4.3 ± 0.3 (SEM.) months at the time of DPG determinations. DPG was similar in treated patients and in the control subjects: 6.27 ± 0.22 mM/L RBC and 6.16 ± 0.23 mM/L RBC, respectively. The initial PCV was also similar: 21.72% ± 1.36 and 20.13% ± 0.91. Although the mean PCV during treatment was higher for 5 of 9 ND-treated patients (p < 0.01), the final PCV prior to termination of therapy was greater than the initial pretreatment PCV in only 2 of these 5 patients (p > 0.05). We conclude that 200 mg ND weekly has no effect on the red cell DPG and a transient unsustained effect in raising the PCV in male chronic hemodialysis patients over a 5-month period of treatment.