Early recognition of alcohol problems by general practitioners might be enhanced by the use of better alcohol markers. Several studies have revealed promising results for the carbohydrate-deficient transferrin (CDT) assay in certain populations. The aim of our study was to examine the specificity of the CDT assay in a general practice population. The main research question was whether common chronic diseases and/or the accompanying prescribed drugs have a negative influence on the specificity of the CDT assay. The 524 men who participated were selected from seven general practices and were suffering from one or more of the following diseases: hypertension, asthma/bronchitis, diabetes mellitus, adipositis/lipid metabolism disorder, angina pectoris, depression, and disorders of the digestive tract. None of the studied diseases or of the accompanying prescribed drugs had an influence on the specificity of the CDT assay. The overall specificity in this general practitioner population was 0.92. It can be concluded that the studied diseases do not bear an influence on the serum CDT concentration, and that, therefore, the CDT assay is a highly specific instrument for use in assessing alcohol consumption in general practice patients.