Reducible compounds that participate in crosslinking were analyzed in hydroxylysine-deficient collagens of patients with a heritable disorder of connective tissue. After treatment with [(3)H]sodium borohydride, new compounds, as well as a totally different pattern of tritiated compounds, were found in hydroxylysine-deficient collagen from skin as compared with age-matched controls. The amount of desmosines detected indicated that more elastin was present in abnormal skin than in control skin.Bone collagen, which was not as deficient in hydroxylysine as skin collagen, had the same compounds as normal bone collagen, but their relative proportions were altered, consistent with a deficiency of hydroxylysine, a precursor of the crosslinks. Although the content of hydroxylysine in collagen of cartilage is essentially normal in these patients, analysis after reduction revealed a different pattern of reduced compounds from that of normal cartilage. It is speculated that Type II collagen, the major collagen component in cartilage, contains a normal amount of hydroxylysine, while Type I collagen, which is the major source of the crosslinks, is hydroxylysine-deficient. This distribution would explain the findings of an abnormal profile of reducible compounds despite an almost normal total hydroxylysine content. The finding that the deficiency of hydroxylysine in the collagen of these patients is accompanied by changes in number, chemical nature, and, probably, distribution of crosslinkages, and the previously reported alterations in the solubility characteristics, suggest that at least some skeletal and connective tissue abnormalities are directly related to underlying molecular pathology.