Pregnant female albino rats were treated orally with lithium carbonate dissolved in distilled water. Treatment at 100 mg/kg day 16 until day 20 of gestation caused marked maternal toxicity including polyuria. For the progeny increased rates of prenatal and postnatal mortality were noted. In part of the progeny sacrificed near term by Caesarean section, the visceral examination of the fetuses revealed an enlargement of the renal pelves in association with rudimentary or missing papillae. The renal anomalies are interpreted as being consistent with a developmental retardation due to specific lithium activity. After birth, i.e. after termination of maternal treatment, slight to moderate structural changes of the kidney were apparently compensated. 60 mg/kg through days 16-20 of pregnancy caused moderate maternal toxicity including polyuria. The offspring showed a postnatal development near the normal range, however, and no renal anomalies were recorded. In the view of the nephrotrophic property of lithium as known for the adult rat, the results indicate that possible transplacental effects on the fetal kidney as a target organ should be also considered.