Lysyl oxidase, the enzyme responsible for mediating crosslink formation in collagen and elastin, requires copper for its activity. In this study, lysyl oxidase activity and insoluble elastin content were unchanged in lungs from copper-deficient hamsters compared to controls. The lack of dramatic diminution in lysyl oxidase activity in animals who demonstrate significant structural alterations in the lung suggests that other mechanisms in addition to inhibition of crosslink formation are operative in this model.