Abstract:Sixty female Wistar‐Imamichi rats, each weighing 85 gm, were divided into 10‐rat groups and fed respectively (by mouth) daily for four weeks: corn oil; dihydrotachysterol (DHT), 50 μg; DHT + conjugated estrogens (Premarin), 25 μg; DHT + Premarin, 100 μg; Premarin, 25 μg; or Premarin, 100 μg. Data were collected on body and organ weights; the calcium content of serum, aorta, heart, kidney and femur; x‐ray examination of the tail bone; and histological changes in the tissues involved.Under the experimental conditions, administration of DHT caused marked hypercalcemia and a significant increase in the calcium content of the kidney and heart. On the other hand, the calcium content of the femur in the rats treated with DHT was markedly decreased as compared with that in the controls. Histological and radiological evidence indicated that the administration of DHT was associated with increased bone resorption, subsequently developing into osteoporosis.All these DHT‐induced changes were prevented by the simultaneous administration of Premarin. Thus conjugated estrogens apparently prevent the development of the “progeria‐like syndrome” in rats—a syndrome which is quite similar to premature aging. The possibility of a relationship to slowing of the aging