The objective of this paper is to consider several categories of biomarkers of human pregnancy. The design of the report is to discuss useful and promising markers and techniques. Research gaps, needs, and priorities are also defined. Useful markers are mixed lymphocyte culture reactions, measures of lymphocytotoxic antibodies, histocompatibility (HLA) typing, and immunohematological evaluations. Promising markers are measures of major basic protein and early pregnancy factor, as well as determinations of trophoblast-lymphocyte cross-reactive (TLX) antigens. Promising techniques are fluorescence-activated cell-sorter analysis of maternal blood for fetal and extraembryonic tissues and immunotherapy with TLX and other antigens to prevent spontaneous abortion. It is concluded that immunology has much to offer the development of biomarkers of human pregnancy.