CHICAGO, Aug. 19 - The Illinois State Police canceled its contract for DNA analysis with the Bode Technology Group after finding that it failed to recognize semen on evidence in 22 percent of cases that were checked again by forensic scientists who work for the police.

Out of a random sample of 51 cases that were re-analyzed for quality assurance, the police said 11 tested positive for the existence of semen. They plan to test all 1,200 cases that Bode Technology said tested negative for semen and are asking the state attorney general for permission to sue the company.

"The work provided by Bode was imprecise and we can't tolerate that type of work in this business," Larry Trent, the state police director, said at a news conference on Friday. "I'm outraged that a company with their reputation would conduct business in this manner, and we're not going to let them get away with it."

Mr. Trent sent letters to the Justice Department and to top law enforcement officials in every state on Friday to notify them of the findings. He said the Justice Department and at least 10 states had contracted with Bode for forensic analysis.