In this AIDS Commentary, Dr. Catherine Wilfert addresses the issue of vertical transmission of the human immunodeficiency virus type 1 (HIV-1). She reviews the results of the recently completed trial conducted by the AIDS Clinical Trials Group that evaluated the effectiveness of administering zidovudine to pregnant women in reducing the incidence of vertical transmission. In view of the success of this trial, Dr. Wilfert addresses the problem of the efficacy of voluntary counseling and testing of pregnant women. Identification and treatment of HIV-1 infected women could potentially reduce the incidence of pediatric HIV-1 infection and increase the number of women receiving appropriate therapy. She makes the point that legislative mandates have been necessary to produce rates of childhood immunization that are effective in reducing the occurrence of vaccine-preventable diseases. This suggests that such mandates are an option to consider in the effort to control vertical transmission of HIV-1 infection. Her cost-benefit analysis indicates that universal screening of pregnant women for HIV infection would result in enormous overall savings for the health care system. Obviously, making the testing of pregnant women mandatory raises a number of difficult issues and is controversial. Dr. Wilfert has provided a service by raising this issue; further discussion is needed.