The “pregnancy zone” serum protein was found in 73 out of 145 women (50%) taking oral contraceptive drugs. There was a significant difference with respect to the frequency with which the “pregnancy zone” was induced by different types of contraceptives. Conlunett produced the “pregnancy zone” in 64% of the women and Follinyl in 38%. This difference may reflect the composition of the pills. A history of previous pregnancies or the duration of administration of the hormones had no significant effect on the induction of the “pregnancy zone”.