D-pencillamine, a stable not physiological amino acid, has a manifold mode of action. Of special importance there is its influence on the collagen-metabolism, the gelose of heavy metals and the effect on immunologic processes. The use of D-penicillamine is possible in different diseases, such as Wilson's syndrome, collagenoses of diverse kinds, especially the rheumatoid arthritis, further chronic hepatitis and lung fibrosis. In this paper we report about 52 children, who were treated with D-penicillamine. The biggest group presented chronic liver diseases in 24 patients and rheumaoid arthritis in 21 patients. The therapy was carried out for a longer time, in some cases over years. The dose varied from 15 to 35 mg/kg of body weight. The number of side-effects was lower in children than in adults. They were more frequent in the group of collagenoses than in the group of liver diseases. Whether later on liver damages will occur is not predictable by the pediatrician. The results were excellent for the chronic active hepatitis; we can recommend D-penicillamine for such affections. Also for the rheumatoid arthritis we could partially obtain good successes, but not as convincing as in liver-diseases.