Aminomethylphosphonic acid (CAS No. 1066-51-9) was evaluated for developmental effects in groups of 25 female Charles River rats administered the test substance by gavage at dose levels of 0, 150, 400, or 1000 mg/kg/day in a constant dose volume of 10 mL/kg in corn oil on days 6 through 15 of gestation. Animals were sacrificed on day 20 of gestation. Clinical signs of toxicity at 400 and 1000 mg/kg/day included mucoid feces, hair loss and soft stool. Mean body weight gain was slightly reduced during days 12 through 16 of gestation at 1000 mg/kg/day (p<0.05). The 1000 mg/kg/day group showed slightly decreased mean fetal body weight. No treatment related fetal malformations or developmental variations were observed at any of the dose levels. The NOAEL was 150 mg/kg/day.