No significant differences of Km or Vmax could be demonstrated for the initial rate (0–3 min) of iron uptake by preparations of isolated duodenal mucosal epithelial cells from normal or sex-linked anemic (sla) mice. Isolated cells from sla mice do, however, take up significantly more iron than normal cells after 20-min incubation. Upon reincubation with various types of mobilizing agents, the amount of iron released from, and the amount of iron remaining in, cells from sla mice was significantly elevated compared to control values. The percentage of iron released was the same for both types of cells, for all mobilization media employed. The current data, in conjunction with previous studies that showed deficient mucosal to serosal transport of iron in everted duodenal sacs from sla mice, suggest that the lesion in these mice may be located between the mucosal cell and the vascular compartment rather than in the mucosal cell.