As more women of childbearing age are being identified as HIV infected, vertical transmission to the fetus and/or neonate is an increasingly significant therapeutic problem. Currently the use of zidovudine is one of the few specific measures available, and as a potentially teratogenic and fetotoxic agent, any decision for its use requires evaluation of the potential for fetal damage. In a series of 104 cases of intentional or inadvertent use of zidovudine at differing gestations in pregnancy, there were eight spontaneous first trimester abortions, eight therapeutic terminations, and eight cases of fetal abnormality occurring among a total of 88 cases where the pregnancy progressed. Analysis and correlation of antenatal data and drug therapy with individual cases failed to show any specific abnormality that could reasonably be attributed to zidovudine therapy. While not proving safety, these data add to previous smaller series with similar findings, thus lending tenuous support to the use of this agent. Continuing studies are required, particularly to clarify the possibility of long-term developmental defects.