Nurses increasingly work as substitutes for, or to complement, general practitioners in the care of minor illness and the management of chronic diseases. Available research suggests that nurses can provide as high quality care as GPs in the provision of first contact and ongoing care for unselected patients. Reductions in cost are context dependent and rarely achieved. This is because savings on nurses' salaries are often offset by their lower productivity (due to longer consultations, higher patient recall rates, and increased use of tests and investigations). Gains in efficiency are not achieved when GPs continue to provide the services that have been delegated to nurses, instead of focusing on the services that only doctors can provide. Unintended consequences of extending nursing roles include loss of personal continuity of care for patients and increased difficulties with coordination of care as the multidisciplinary team size increases. Rapid access to care is, however, improved. There is a high capital cost involved in moving to multidisciplinary teams because of the need to train staff in new ways of working; revise legislation governing scope of practice; address concerns about legal liability; and manage professional resistance to change. Despite the unintended consequences and the high costs, extending nursing roles in primary care is a plausible strategy for improving service capacity without compromising quality of care or health outcomes for patients.