Two brothers with familial erythrocytosis born to parents of a consanguinous marriage are described. Two other siblings were unaffected. There was a marked increase in erythropoietin concentration in both the plasma and urine, suggesting that a congenital defect led to erythropoietindependent polycythemia. Other causes of polycythemia were excluded.

  • Submitted July 24, 1972.
  • Revision received January 2, 1973.
  • Accepted February 4, 1973.