Metal-chelating drugs were employed to investigate the role of copper (Cu) in elastin metabolism during the period of alveolarization in rat lung. Six groups of pregnant Sprague-Dawley rats were fed one of six semipurified diets, i.e., sufficient or deficient in copper, or the same basal diet containing 0.2% or 0.4% D-penicillamine (DPA), or the same basal diet containing 0.2% or 0.4% triethylenetetramine (TETA). The dams were fed throughout gestation, parturition, and lactation. The pups were then killed postnatally at day 10 and day 21 for the various analyses. At day 21, liver copper in the Cu-deficient pups was 3-5% control levels. In drug-treated groups, liver copper was 16-30% control levels. In the 21-day-old Cu-deficient rats, the concentration of lung elastin was only 75% of its concentration in control. Lung lysyl oxidase activity was lower in Cu-deficient rats, and data for the relative distribution of lung elastin cross-linking amino acids indicated impaired cross-linking in the pups from both the Cu-deficient and the 0.4% DPA groups. Morphologic examination of the lung also indicated dilation of airways in these two groups. Data on the distribution of cross-linking amino acids in elastin samples were also consistent with previous suggestions that impaired cross-linking observed in copper deficiency or from DPA treatment results from different mechanisms. Since the intakes of DPA and TETA were chosen to be in the therapeutic range of intakes used to treat diseases of abnormal copper metabolism, an important feature of these studies is that DPA and perhaps TETA have the potential of impairing normal lung development.