High rates of untreated mental illness cause serious health problems in the United States and worldwide. The use of computer-administered therapy has the potential to increase access to mental health care for certain patient populations. An online version of an alcohol check-up was developed that guided subjects through a series of standardized questionnaires, and provided them with feedback designed to enhance their appreciation of the negative aspects of their alcohol use. Ratings of the helpfulness of the questionnaires were evaluated in order to determine the characteristics of individuals who would potentially benefit from an automated substance abuse intervention, and to learn which aspects of an automated program would be most useful. Over a period of 25 months, 1,455 individuals participated in the study, 83% of whom had an Alcohol Use Disorders Identification Test (AUDIT) score indicative of problem drinking. Subjects with alcohol problems found the on-line program more useful than other subjects. The questionnaire which compared subjects' alcohol use to national norms, provided the most helpful and also the most unexpected information. Alcohol abusers with high levels of ambivalence about their drinking and other measures of motivation for change found the program more helpful than those with lower motivation. Automated therapy made available to the general public via the Internet can be accessed by large numbers of individuals. The interaction can be useful to patients with significant levels of substance abuse.