Because a previous study among 385 psychiatric admissions had shown each of three rapid interviews to be far superior to each of nine laboratory tests in screening for excessive drinking and alcoholism, the separation of patients with these drinking patterns from normal drinkers was reexamined by the more sophisticated technique of discriminant analysis. It was thus possible to determine where there was overlap in the information provided by some tests in contrast to "new information" provided by others and whether the arbitrary cut-off points of the normal ranges of the laboratory tests were contributing to their poor sensitivity. Discriminant analysis again confirmed the good performance of the rapid interviews, particularly the Brief Michigan Alcoholism Screening Test and the Reich interview, but it also identified glutamate dehydrogenase (GDH) as the best of the laboratory tests and of comparable efficacy to the rapid interview for the group of excessive drinkers. By comparison, gamma-glutamyl transpeptidase and mean corpuscular volume performed poorly. Using the whole range of results rather than a single cut-off point for discriminant analysis did not alter the relative performance of the screening tests. The optimum combination of tests was that of the Reich interview and the GDH, achieving 100% sensitivity for excessive drinking and alcoholism without any decline in the specificity or predictive value of a positive test result.