The clinical findings and biochemical studies are described for a 30-year-old man with Ehlers-Danlos syndrome. Type analysis of collagen produced by cultured fibroblasts revealed the lack of a detectable pro alpha 2 chain of type I procollagen. The intracellular degradation rate of newly synthesized collagen was higher than that of normal cells, resulting in the reduction of net collagen production. Clinical manifestations characterized by cardiovascular abnormalities due to decreased collagen deposition in the aortic valve and the wall of aorta, hypermobility of the joints, and hyperextensibility of the skin in this patient may be closely related to the observations described above.