At the turn of the 20th century, Mendel's laws were found to be applicable to human blood groups. Within two decades, blood group genetics were applied to problems of parentage. Expansion of immunohematology into leukocyte antigen identification produced the single most informative, expressed polymorphism. About the same time, analysis of a great number of soluble protein polymorphisms followed advances in electric separation methods, enzymology, and immunochemistry. As new, independent loci were discovered, the power to exclude the falsely accused increased, and it became possible to apply Bayesian principles to determined probabilities of biologic relationships. The revolution in nucleic acid technology has dramatically improved analysis and statistical inferences. By the turn of the 21st century, laboratories should be able to determine biologic parentage with virtual certainty.