The potential for neurotoxic effects was evaluated in rat off-spring after exposure in utero and/or during the neonatal period to a recombinant subunit vaccine of gp120 prepared from the MN strain of HIV-1 (MN rgp 120/HIV-1). Thirty pregnant female rats were given MN rgp120/HIV-1 with alum adjuvant, and 30 rats were given vehicle, once every 3 days from Day 1 of presumed gestation until parturition. One pup/sex/litter from treated and control group dams were given a daily subcutaneous injection, from Day 1 through Day 22 postpartum (PP) of vehicle, MN rgp120/HIV-1, MN rgp120/HIV-1 with alum, or MN rgp120/HIV-1 with QS-21 adjuvant. Neurobehavioral and physical development were evaluated (preweaning reflex and development, sexual maturation, motor activity, acoustic startle, passive avoidance, functional observational battery, and water M-maze testing), and tissues were processed for anatomical examination (whole and regional brain weights, and neuropathology). Administration of MN rgp120/HIV-1, with or without adjuvant, to pups did not cause any persistent effect on any parameter evaluated. Neurohistological examination did not reveal any pathological effects related to treatment. Thus, MN rgp120/HIV-1 alone or formulated as a vaccine does not cause neurotoxicity or developmental toxicity in neonatal rats after exposure in utero and/or during the neonatal period.