The action of D-penicillamine on collagen can cause undesired side-effects in the treatment of cystinuria and Wilson's disease, it is on the other hand essential to the therapy of rheumatoid arthritis and scleroderma. Furthermore D-penicillamine can be potentially teratogenic, since it crosses the placental barrier. From the literature and our own observation of two pregnancies it is shown that among 87 pregnant women who received D-penicillamine 46 cases were treated during the whole period of pregnancy. Two infants from the latter group were found to have severe connective-tissue defects. We suggest that the dose of D-penicillamine in pregnant patients with cystinuria and Wilson's disease should be kept as low as possible. In the case of rheumatoid arthritis D-penicillamine should not be given during pregnancy.