Several recent reports have described alterations in collagen metabolism in certain heritable diseases in man. These studies reflect the rapid increase in our understanding of the structure and synthesis of collagen, as well as technical advances that allow the characterization of the collagen present in small biopsies of tissue and in fibroblast cultures. So far, most of the defects identified are recessive traits involving enzymes that modify the primary structure of collagen, although defects in the synthesis of one or another of the genetically distinct tissue collagens (Table 1) are suspected. The most extensive studies have been done on patients