Objective: To evaluate the efficacy and relative costs of different screening methods for the identification of alcohol use disorders in an opportunistic screening programme in primary care in the United Kingdom. Design: Comparative study. Setting Six general practices in south Wales. Participants 194 male primary care attendees aged 18 or over who completed an alcohol use disorders identification test (AUDIT) questionnaire. Main outcome measures: Scores on alcohol use disorders identification test and measures of gamma-glutamyltransferase, aspartate aminotransferase, per cent carbohydrate deficient transferrin, and erythrocyte mean cell volume. Hazardous alcohol consumption, weekly binge consumption, and monthly binge consumption were ascertained using the time line follow back method over the previous 180 days. Alcohol dependence was determined using the Diagnostic and Statistical Manual of Mental Disorders, fourth edition. Unit costs were established from published resource references and from actual costs of analysing the biochemical tests. Results: A significant correlation was observed between alcohol consumption and score on the alcohol use disorders identification test (Pearsons correlation coefficient r = 0.74) and measures of gamma-glutamyltransferase (r = 0.20) and per cent carbohydrate deficient transferrin (r = 0.36) but not aspartate aminotransferase (r = 0.08) or erythrocyte mean cell volume (r = 0.02). The alcohol use disorders identification test exhibited significantly higher sensitivity, specificity, and positive predictive value than all of the biochemical markers for hazardous consumption (69%, 98%, and 95%), weekly binge consumption (75%, 90%, and 71%), monthly binge consumption (66%, 97%, and 91%), and alcohol dependence (84%, 83%, and 41%). The questionnaire was also more cost efficient, with a lower cost per true positive for all consumption outcomes. Conclusion: The alcohol use disorders identification test questionnaire is an efficient and cost efficient diagnostic tool for routine screening for alcohol use disorders in primary care. (Author' s abstract)