The Michigan Alcoholism Screening Test (MAST), devised to provide a consistent, quantifiable, structured interview instrument to detect alcoholism, consists of 25 questions that can be rapidly administered. Five groups were given the MAST: hospitalized alcoholics, a control group, persons convicted of drunk driving, persons convicted of drunk and disorderly behavior, and drivers whose licenses were under review. The validity of the MAST was assessed by searching the records of legal, social, and medical agencies and reviewing the subjects' driving and criminal records. The MAST responses of 15 subjects who were found to be alcoholic in the record search were analyzed to determine where the screening failures had occurred. Recommendations are made for reducing the number of such "falsė negatives."