The basic aspects of the mechanical process(es) responsible for follicle rupture and ovum expulsion require further clarification. Previous studies have shown that ovarian smooth muscle contractions and prostaglandins are associated with the ovulatory process. Ovarian con-tractility increases during the periovulatory interval in the rabbit and is affected by the hormonal milieu in both the rhesus monkey and human. Prostaglandin synthesis inhibitors (e.g., indomethacin) and antihistamine are associated with an inhibition of both ovarian contractions and ovulation. During the use of indomethacin, however, ovarian steroido-genesis persists apparently unaltered. The proposed investigations are designed to evaluate ovarian smooth muscle activity and local require-ments at the ovarian level preceeding and during the ovulation process. The approaches used will include: 1) studies of ovulation in the in vitro perfused rabbit ovary; 2) alterations of the constituents of the perfusate delivered to the rabbit ovary; 3) biochemical evaluation of the perfusate and ovarian effluent; 4) measurements of ovarian contractile activity in the in vitro perfused rabbit ovary under a variety of circumstances; 5) adaption of the perfusion preparation for the study of in vitro ovulation in the primate ovary; and 6) continuation of studies of ovarian contractility in the rhesus monkey using chronically implanted intra-ovarian transducers. These interrelated studies will provide basic information regarding the mechanism of ovulation and the local requirements essential for the occurrence of this process.