Clinical medicine in the 21st century is almost certain to include wide-scale use of molecular genetic diagnostic tests. In September 1986, The Johns Hopkins University School of Medicine initiated a voluntary program of presymptomatic genetic testing for Huntington's disease for persons at 50% risk. DNA analyses using the D4S10 (G8), D4S43, and D4S95 locus probes have been performed for 55 people. Twelve of the tests have yielded positive results, 30 were negative, and 13 were uninformative. Initial reactions ranged from joy and relief to disappointment, sadness, and demoralization. Thus far, there have been no severe depressive reactions. Although the sample size is small, our data suggest that people who receive genetic test results cope well, at least over the short term, when the testing is performed in a clinical context that includes education, pretest counseling, psychological support, and regular follow-up.