Benzidine is a manufactured chemical that does not occur in nature. In the past, large amounts of benzidine were used to produce dyes for cloth, paper, and leather. It was also used in clinical laboratories for detecting blood, as a rubber-compounding agent, and in the manufacture of plastic films. However, benzidine has not been sold in the United States since the mid-1970s, and it is no longer used in medical laboratories or in the rubber and plastics industries.