To the Editor: In 1967, an interesting article appeared in Nature (Nature [Lond] 215:1139–1142, 1967) by Isaacs and Hayhoe, describing stabilization of the red-cell membrane in sickle-cell disease by certain steroidal preparations. According to the authors, in vivo experiments showing inhibition of sickling in susceptible persons were performed by administration of 17-hydroxyprogesterone or testosterone to the appropriate sexes. Subsequent serial blood samples were exposed to sodium metabisulfite, with failure of distortion of the red cells over variable periods and evidence from phase microscopy of the customary tendency toward rearrangement of hemoglobin molecules persisting. Medroxyprogesterone (Depo-Provera) was found by us to . . .