The effect of D-penicillamine (DPA) on the development of lung and kidney tissues was evaluated to determine whether the association of lung and kidney malformation results from a common generalized disorder of connective tissue in the fetal rat. Ten animals received a daily dose of 300 mg DPA in their drinking water during the last six days of their gestation. Ten other pregnant rats were used as controls. At the end of the gestation period all the animals were delivered by cesarean section. We found that DPA treatment during gestation caused marked growth retardation in the offspring. Although the lung weight to body weight ratios did not differ between the study and control groups, the left-kidney weight to body weight ratios were found to be lower in the study group. Histologic sections showed pulmonary dysplasia with bronchomegaly, cystic alveoli, atelectasis, vascular aneurism, perivascular loose of connective tissue, small hemorrhagic foci in the lungs and caliechtasis. We hypothesize that a common connective tissue disorder induced by DPA during intrauterine life may cause lung and kidney malformations.