Prenatal diagnosis of hematologic diseases can now be performed with fetal blood, fetal amniotic fluid cell DNA, and fetal chorionic villi DNA. Some hemoglobinopathies can be detected by all three methods, and the choice will depend on the available obstetric and laboratory techniques, as well as the time of presentation of the pregnancy. Hopefully, further development of molecular probes and techniques will soon expand these options to all of the globin disorders. Detection of coagulation disorders in utero currently requires samples of pure fetal blood. Gene cloning is accomplished for some (factor IX and antithrombin III) and is underway for others (factor VIII), and further investigation is necessary to determine whether deficiencies in these gene products are due to gene deletion or to mutant genes linked to polymorphic restriction enzyme sites of diagnostic use. Thus, molecular biology may be applied to prenatal diagnosis of the clotting problems, but this has not yet been accomplished. Disorders affecting the number and/or function of erythrocytes, leukocytes, and platelets can be diagnosed by analysis of fetal blood. Blood samples will continue to be required until more is known about the molecular biology of hematopoiesis. Syndromes that can be diagnosed by chromosome studies should be revealed in cultures of amniotic fluid cells, fetal blood lymphocytes, and chorionic villi cells. Cultured cells can be examined for karyotypes, Y-chromatin, spontaneous or induced chromosome breakage, DNA repair, SCEs, and translocations. The techniques for culturing amniotic cells and fetal blood white cells are established, and those for growing cells from chorionic villi are improving rapidly. Direct preparations of cells from villi only may suffice for some of the above analyses. The study of hematologic disease in utero has thus come full circle, from the use of amniotic cells to determine the sex in X-linked disorders, to fetal blood sampling for the analysis of gene products, then back to amniocentesis for DNA, and now earlier in gestation to chorionic villi. All of this has occurred in less than ten years, and it is anticipated that developments in the next ten years will be equally dramatic. The future should bring all prenatal testing into the first trimester, use molecular probes, and provide for both early diagnosis and early treatment of genetic hematologic disease.