Although a number of studies have suggested that hostility and drug dependence may be related, there are few systematic studies of this issue. Using the Hostility and Direction of Hostility Questionnaire, the present study compares several drug-dependent groups of patients. Results showed that the intravenous in-patient group was more hostile on several variables than their out-patient counterparts, and also more hostile than an oral in-patient group. Barbiturate abusers were found to have high levels of hostility; amphetamine abusers were the least hostile group, and narcotic dependent patients were intermediate between the two. Correlations between scales of the HDHQ, were all positive, and most were both high and statistically significant, suggesting that hostility represents a relatively generalized trait in drug-dependent subjects. The results are discussed both in terms of patient selection factors—the differential pressures on different types of patients, and in terms of direct drug effects. It is suggested that the hostility of drug-dependent patients may represent an important problem of personal functioning and may require special attention in treatment programmes.