Lead nitrate alone or lead chelated with ethylene-diaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), iminodiacetic acid (IDA), and penicillamine (PEN) was administered iv to pregnant rats on days 9, 11, or 16 of gestation (day 1 = vaginal plug) at a 1:1 molar ratio of chelating agent to lead at a dosage of 35 or 50 mg/kg with respect to lead nitrate. Lead nitrate alone caused resorptions and fetal malformations on day 9, resorptions on day 11, and resorptions and hydrocephalus following treatment on day 16. The lead-chelate complex either reduced or equaled but did not enhance the overall embryo or fetal toxicity. There were no qualitatively different effects produced with chelated lead versus lead alone. The chelating agents were more effective after treatment on gestation day 9 that after days 11 or 16. Ethylenediaminetetraacetic acid produced the greatest reduction in overall effect, with PEN and NTA intermediate, while IDA provided the least overall protective effects.