A single injection of hexoestrol, 45 mg., is effective in suppressing lactation. Given in this way hexoestrol causes a small rise in plasma factor IX levels, of shorter duration than that produced by a customary and equally effective oral course of stilboestroL With hexoestrol the plasma factor IX levels reverted to normal by the sixth day of the puerperium. © 1969, British Medical Journal Publishing Group. All rights reserved.