OBJECTIVE--To compare the process and outcome of "primary care" consultations undertaken by senior house officers, registrars, and general practitioners in an accident and emergency department. DESIGN--Prospective, controlled intervention study. SETTING--A busy, inner city accident and emergency department in south London. SUBJECTS--Patients treated during a stratified random sample of 419 three hour sessions between June 1989 and May 1990 assessed at nurse triage as presenting with problems that could be treated in a primary care setting. 1702 of these patients were treated by sessionally employed local general practitioners, 2382 by senior house officers, and 557 by registrars. MAIN OUTCOME MEASURES--Process variables: laboratory and radiographic investigations, prescriptions, and referrals; outcome variables: results of investigations. RESULTS--Primary care consultations made by accident and emergency medical staff resulted in greater utilisation of investigative, outpatient, and specialist services than those made by general practitioners. For example, the odds ratios for patients receiving radiography were 2.78 (95% confidence interval 2.32 to 3.34) for senior house officer v general practitioner consultations and 2.37 (1.84 to 3.06) for registrars v general practitioners. For referral to hospital specialist on call teams or outpatient departments v discharge to the community the odds ratios were 2.88 (2.39 to 3.47) for senior house officers v general practitioners and 2.57 (1.98 to 3.35) for registrars v general practitioners. CONCLUSION--Employing general practitioners in accident and emergency departments to manage patients with primary care needs seems to result in reduced rates of investigations, prescriptions, and referrals. This suggests important benefits in terms of resource utilisation, but the impact on patient outcome and satisfaction needs to be considered further.