The effect of the concentration of (⋄) DFO, (○) PIH, and the PIH analogues (⬡) 206, (▪) 308, (▴) 309, (•) 311, and (▿) 315 on internalized ⁵⁹Fe uptake from ⁵⁹Fe-Tf (1.25 μmol/L) by SK-N-MC NB cells over 3 hours of incubation at 37°C. After this, the cells were washed and the internalized ⁵⁹Fe was determined by incubation with pronase (1 mg/mL) for 30 minutes at 4°C. The results are means of duplicate determinations from a typical experiment.