OBJECTIVES--To compare outcome and costs of general practitioners, senior house officers, and registrars treating patients who attended accident and emergency department with problems assessed at triage as being of primary care type. DESIGN--Prospective intervention study which was later costed. SETTING--Inner city accident and emergency department in south east London. SUBJECTS--4641 patients presenting with primary care problems: 1702 were seen by general practitioners, 2382 by senior house officers, and 557 by registrars. MAIN OUTCOME MEASURES--Satisfaction and outcome assessed in subsample of 565 patients 7-10 days after hospital attendance and aggregate costs of hospital care provided. RESULTS--Most patients expressed high levels of satisfaction with clinical assessment (430/562 (77%)), treatment (418/557 (75%)), and consulting doctor's manner (434/492 (88%)). Patients' reported outcome and use of general practice in 7-10 days after attendance were similar: 206/241 (85%), 224/263 (85%), and 52/59 (88%) of those seen by general practitioners, senior house officers, and registrars respectively were fully recovered or improving (chi2 = 0.35, P = 0.840), while 48/240 (20%), 48/268 (18%), and 12/57 (21%) respectively consulted a general practitioner or practice nurse (chi2 = 0.51, P = 0.774). Excluding costs of admissions, the average costs per case were 19.30 pounds, 17.97 pounds, and 11.70 pounds for senior house officers, registrars, and general practitioners respectively. With cost of admissions included, these costs were 58.25 pounds, 44.68 pounds, and 32.30 pounds respectively. CONCLUSION--Management of patients with primary care needs in accident and emergency department by general practitioners reduced costs with no apparent detrimental effect on outcome. These results support new role for general practitioners.