Experimental arteriosclerosis that closely resembles human arteriosclerosis was produced by a deficiency of pyridoxine and essential fatty acids in monkeys subjected to a synthetic diet. A detailed analysis of the pathological changes in the various organs disclosed that the changes produced differed in severity as follows: deficiency of both pyridoxine and essential fatty acids produced the most severe changes, then pyridoxine deficiency alone and then essential fatty acids deficiency alone.