Historically, professional and societal debate regarding drug taking, drug use problems, and the usefulness of drug testing programs occurs in cycles. Analytical methods commonly used to test for drug use include breath analysis for alcohol and urinalysis. Blood alcohol concentrations are determined by laboratory assay methods or by portable devices used in the field. While poor laboratory procedures can invalidate test results for both breath and urine tests, urine screening test results can b further invalidated by the improper handling of specimens or by tampering by the person tested. Also, test results are meaningful only if correlated with a clinical state. Legal issues have been raised concerning the validity and reliability of testing, especially in relation to preemployment drug screening.(Author abstract modified)