The CAGE questionnaire, a mnemonic for attempts to cut back on drinking, being annoyed at criticisms about drinking, feeling guilty about drinking, and using alcohol as an eye opener, was used as a screening instrument. The mean corpuscular volume of red blood cells, liver transaminase levels, and gamma-glutamyl transpeptidase levels were also evaluated as screening tests. The presence or absence of alcoholism and alcohol abuse for a consecutive sample of CAGE-negative patients and all patients answering affirmatively to one or more CAGE questions was established by administering the Michigan Alcoholism Screening Test, a detailed chart review, and analysis of the quantity of consumed alcohol. The prevalence of alcohol abuse among the 518 patients was 20 percent. The mean corpuscular volume, gamma-glutamyl transpetidase value, and liver transaminase levels were very insensitive as screening tests. In contrast, the CAGE questionnaire had a sensitivity of 85 percent and a specificity of 89 percent. Only 63 percent of the alcoholic subjects and alcohol abusers were detected by their physicians; physicians addressed the problem in only 24 percent of the cases. The authors conclude that the CAGE questionnaire is a simple, sensitive, and specific screening test for alcohol abusers. 19 references, 3 tables, and 1 figure