An attempt was made to study the relationship between secondary anemia and the reticuloendothelial uptake in 18 patients with cancer. The RE up- take of colloidal radiogold was significantly more rapid in the patients than in the controls; so was the plasma clearance of radioiron even though there was not any statistically significant anemia. The gold and iron clearances were significantly correlated to each other, and to the erythrocyte sedimentation rate. The results are considered to be compatible with the hypothesis that cancer anemia may be caused, e.g., by RE uptake of some erythropoietic substances and of erythrocytes.