The value of urine tests for determining an equivalent blood alcohol concentration in driving under the influence (DUI) enforcement cases is reviewed from a historical, theoretical, and practical perspective. The limits of precision and accuracy that can be ascribed to urine alcohol results are demonstrated through an evaluation of actual case results wherein both a first void and a subsequent urine sample were analyzed and converted to an equivalent blood alcohol concentration (BAC) using a urine to blood conversion factor of 1.3:1.