ABSTRACT In an attempt to analyze the specific phases in the chain of reproductive events which might be susceptible to controlled immunological interference, a brief review is given of some of the current concepts of the physiological regulation of the cardinal steps of the human reproductive process, such as spermatogenesis, epididymal sperm maturation, ovulation and the menstrual cycle, sperm transport in the female organism, capacitation, fertilization, tubal transport of the fertilized ovum, implantation and early embryonic development. The necessary prerequisites for the large scale use of a safe immunological method seem to suggest that an in-depth study of the specific constituents of unique biologically active principles (enzymes, hormones) present in suitable extracts of human sperm and/or human placenta might offer an attractive lead for the development of fertility regulating methods based on active immunization.