Objective: To investigate the direct impact of specialists on prescribing by general practitioners. Design: Cross-sectional, prescription-based study. Subjects and setting: 88 GPs in the Hunter Urban Division of General Practice, Hunter Valley, NSW. Main outcome measure: Proportions of specialist-initiated prescriptions for eight commonly prescribed drug classes. Results: The proportion of specialist-initiated prescriptions was greatest for proton pump inhibitors (85%), and lowest for diuretics (8%), newer antidepressants (10%) and H2-receptor antagonists (13%). Specialists initiated 29% of prescriptions for beta-blockers, 26% for calcium-channel blockers, 20% for statins and 19% for angiotensin-converting enzyme inhibitors or angiotensin II antagonists. Specialists were more likely to have been involved in starting therapy with metoprolol than other beta-blockers (51% v 23%) and diltiazem than other calcium-channel blockers (48% v 19%), and this was related to indication for treatment. In contrast, prescriptions for the more recently introduced drugs (angiotensin II antagonists and atorvastatin) were not more likely to have been specialist-initiated than prescriptions for established angiotensin-converting enzyme inhibitors and statins. Conclusions: The direct impact of specialists on prescribing in the Hunter Urban Division of General Practice is substantial and varies with the drug class. This highlights the need to engage both GPs and specialists in efforts to improve prescribing practices.