[Dynamics of the action of cyclophosphamide. Studies in the chick embryo]

The dynamics of the Cyclophosphamide (CPA) effect was investigated in the chick embryo by a vital fluorochroming method worked out previously. In the 4-day-old embryo the morphological changes (at the level of light microscopy) in the limbs and in the mesencephalon induced by 100 microgram CPA appeared after a period of latency of about 10 hours. Successive blood control in the same embryo, treated with 50 microgram CPA, revealed three consecutive modifications of the blood cells: a great number of abnormal mitoses, the appearance of a great number of multinucleated, nonviable cells and the recovery of the lost cells. No difference could be detected between the effect of freshly prepared and stored CPA solutions. The fate of CPA (a bifunctionally alkylating agent) in contact with living tissues is discussed.