Fifty-five patients on maintenance hemodialysis underwent bone-marrow aspirations for evaluation of iron stores that were to be compared to concomitant measurements of hematocrit, red blood cell volume, serum iron concentration, total iron binding capacity, transferrin saturation, and serum ferritin concentration. In 42 patients (76.4%), the bone marrow iron stores were found to be absent or deficient. Mean hematocrit for the total group was 26.4%, and red blood cell volume measurement showed a mean value of 41.1% of predicted normal. Results also indicated that serum ferritin was the best predictor of iron storage levels, with diagnostic thresholds of 80 to 350 ng/ml derived from statistical analysis of the data. Other hematologic parameters studied had significantly less correlation with bone-marrow iron stores.