Blind tests require both negative specimens that are free of drugs and positive specimens that contain drugs or drug metabolites. A blind testing program is relatively simple to carry out. The company can purchase specimens from reputable suppliers or hire a company or consultant with expertise in testing. They should also inform the laboratory that they plan to conduct blind testing and share the data obtained with the laboratory. The blind specimens should be indistinguishable from the regular specimens and should make up at least 10 percent of the samples submitted to the drug testing laboratory. Results of the blind tests should be recorded in a separate log book. Users of blind testing programs should be aware that drug tests are accurate, but not infallible and should not change laboratories on the basis of a single error.