Objective: The early events of reproduction involve a carefully modulated complex system of oocyte maturation, fertilization, and proliferation. The aim of the study was to measure the presence of cytokines, namely interleukin 1 (IL-1), interleukin 6 (IL-6), colony-stimulating factor 1 (CSF-1), and tumor necrosis factor (TNF) in the conditioned medium (CM) of the oocytes, granulosa cells, cumulus cells, one to eight-cell embryos and sperm. Design: The material was obtained from men and women undergoing in vitro fertilization therapy. Main Outcome Measures: We hypothesized that cytokines might affect embryonic growth and differentiation as they show a pleotropic effect on immune cells. Results: All these cytokines are present in significant quantities in the CM and were shown to be expressed in a sequential manner; thus, some are present in the oocyte and its vestment, the corona-cumulus complex (IL-1, IL-6, and CSF-1), whereas TNF appears only at the stage of six to eight-cell embryos. Inflammatory cytokines could not be detected in sperm samples. Conclusions: It is possible that these cytokines have a role in the regulation of embryonic development, maternal immunological recognition of pregnancy, and maintenance of proper hormonal environment.