Direction of hostility, as measured by the Hostility and Direction of Hostility Questionnaire, was found to be associated with poor compliance during a treatment trial of a new tricyclic antidepressant. An association with other factors such as the type and severity of depression was not found. There are other studies in the literature which support these observations although some controversy surrounds the role played by personality variables in adherence to treatment. Hostility has been shown to be a possible factor in the aetiology of depression, an important factor in the classification of depression, and a symptom of depression which improves with treatment. Hostility may have a particularly large importance in compliance with treatment for depression or may have been overlooked in studies in compliance with treatment for non-psychiatric disorders.