A 37-year-old white woman with end-stage renal disease due to reflux nephropathy presented with a several-day history of worsening headache. When peritoneal dialysis was begun, 3 months earlier, her hematocrit value was 0.27, and as part of the routine procedure, therapy with epoetin alfa (Epogen) was initiated according to a a pharmacy-approved standard dosing protocol. After 1 month, her hematocrit value had increased from 0.27 to 0.36, and the dosage of epoetin alfa therapy was tapered by 25%, from 7000 to 5000 U. Iron monitoring tests revealed the development of iron deficiency, so the patient was also given intravenous iron therapy. At the end of the second month of therapy, her hematocrit value had increased sharply to 0.50. Again, following the hospital protocol, the dosage of epoetin alfa therapy was reduced 50%, to 2500 U. By the end of the third month of therapy, her hematocrit value had increased to 0.55. At this point, the epoetin alfa therapy was discontinued, and about 2 weeks later, the patient developed a headache, and her hematocrit value decreased to 0.49. At first, she thought that the headache was one of her usual perimenstrual headaches, which she had had for some time, but over a period of 3 to 4 days, the headache became constant and severe.