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SUMMARY In the mouse, a unilateral intra-uterine device (IUD) exerted a bilateral contraceptive effect by causing the elimination of embryos from both uterine horns and the bilateral inhibition of the decidual cell reaction. Both uterine horns showed leucocytic infiltration into the endometrium and uterine lumen. The bilateral effect was correlated with the existence of luminal continuity between the two uterine horns. Conception proceeded normally in the control uterine horn that had been completely separated from the IUD horn. An IUD did not usually disturb the function of the Fallopian tube, but tube-locking of embryos occasionally occurred as an artifact. The contraceptive effects of an IUD were exerted within the uterus during the period immediately before implantation.

Groups of twenty-one IUD and twenty-four control rhesus monkeys were regularly mated with males of proved fertility. None of the IUD females became pregnant, but a total of eighteen pregnancies occurred in fifteen of the control monkeys.A series of observations on the ovaries of control and IUD monkeys examined at laparotomy and autopsy showed that the presence of an IUD affected neither the occurrence nor the timing of ovulation within the natural menstrual cycle.

Summary. This paper describes the techniques used in preparing and supervising rhesus monkeys during a series of experiments to investigate the effects of an intra-uterine device (IUD) upon the processes of conception.Observations made in the course of these experiments established that the presence of an IUD had no biologically significant effect on either the periodicity or the duration of menstruation.

and bilaterality were directly and reliably related to re¬ lief of tremor and rigidity as well as to the postoperative functional status, complications, recurrence, and length of hospitalization.