Practice guidelines aim to guide physician practice according to the best available evidence. Data were mixed regarding the impact of practice guidelines on physician prescribing. The researchers analyzed data from three national ambulatory care surveys to depict long-term trends in U.S. antihypertensive prescribing between 1990 and 2004 in relation to JNC guidelines and short-term trends following the 2002 publication of final ALLHAT results. Seed project findings and findings from additional analysis were consistent with those from the NDTI analysis suggesting that both national guidelines and clinical evidence had an impact on antihypertensive prescribing practices but magnitude of impact may be smaller than desired. Results from this seed project have led to one published manuscript, “Screening, Treatment and Control of Hypertension in U.S. Private Physician Offices, 2003–2004”, in Hypertension.