Under state laws, a medical practitioner will not be found negligent if they acted in a manner that was widely accepted in Australia, by a significant number of respected practitioners in the field, as competent professional practice in the circumstances. This is known as the "peer professional practice defence". The professional opinion being relied on must not be unreasonable (Victoria and Western Australia) or irrational (New South Wales and other states). The peer professional practice defence does not apply to claims of negligence arising from failure to warn patients about risks associated with medical treatment. This reinforces the importance of warning patients of material risks as determined by the High Court of Australia in Rogers v Whitaker. Recent cases demonstrate the successful operation of the peer professional practice defence, but also highlight its limitations. In practice, the legislation may not shield doctors from negligence claims as fully as originally intended.