Effect of phlebotomy on IRP activity in monocytes of GH patients. Monocytes from four unrelated GH patients were isolated before (a) and during (b) phlebotomy treatment and lysates were assayed for IRP activity as described in the legend to Fig 1. The bottom panels report values of serum and monocyte ferritin of the individual subjects. The former were obtained at the time of blood sampling for buffy-coat preparation, the latter were determined in the extract used for bandshift analysis using a radioimmunoassay kit as described in Materials and Methods. Phlebotomy caused a decrease of IRP activity in parallel with reductions of both serum and monocyte ferritin content.