This essay discusses the potential contribution of peritoneal fluid to the regulation of reproductive processes in female mammals. After noting the relatively high concentrations of diverse hormones in peritoneal fluid, and accepting that it bathes the surface of all the internal reproductive organs, peritoneal fluid is then proposed as a means of communication between the two ovaries. It could act to influence both the hierarchy of Graafian follicles and the rate and extent of development of a newly-formed corpus luteum. Cytokines in peritoneal fluid are considered in this context, as are the differing populations of leukocytes. Circumstantial evidence is offered for entry of peritoneal fluid into the Fallopian tubes, especially close to the time of ovulation, with the suggestion that such entry could modify the nature of endosalpingeal secretion and transudation. Thereafter, the spectrum of gonadal hormones in peritoneal fluid could be influencing uterine tissues in a local manner. Finally, reference is made to regional differences in the concentration of steroid hormones in the peritoneal fluid of women, likewise to regional differences in domestic animals.