A Board of Health having advisory functions only was first established under the Public Health Amendment Act 1918, but was quickly superseded by the Board of Health set up by the Health Act 1920. This Board's functions were partly advisory, but it was also given statutory powers to compel local authorities to fulfil their duties under the Act, and where necessary to requisition them to provide sanitary works (water supplies, sewerage, etc.). The Board in fact assumed many of the powers wielded by the District Health Officers under the Public Health Act 1900.

By the Health Act 1956 the composition of the Board was slightly altered but it retains its statutory powers affecting local authorities, and also is required to furnish to the Minister of Health, on request, advice relating to:

1. The adoption of a general health policy for the promotion of health, the prevention of disease and disability, and the adequate and effective treatment of disease, and the proportion of the available resources that should be allocated for each of these purposes.

2. The relationship of the control and management of hospitals to the general health policy.

3. The operation of the health benefits under the Social Security Act 1938, and their relationship to the general health policy.

4. The coordination of the activities of local authorities under the Health Act, and of the activities of voluntary associations in respect of public health with the activities of the Department of Health.

By a new provision, the Board is empowered to appoint committees, of two or more persons, to inquire into and report to the Board on such matters within the scope of its functions as are referred to them by the Board, or to exercise on behalf of the Board any of its powers or functions. Any such committee may include persons who are not members of the Board.

This is a most important and far-reaching provision as the Board is enabled to appoint to such committees persons having special knowledge or qualifications suitable for the purpose for which a committee is appointed. Since 1957 a number of committees have been appointed, to investigate and report on certain matters, and concerned with local authority affairs, fluoridation, services for the deaf, air pollution, epidemiology, maternity services, and Maori welfare. The combined membership of these committees represents a large fund of expert knowledge on a variety of subjects. As a rule the chairman of each committee is a member of the Board, and is able to report personally to the Board on the activity of the committee. Reports of special committees have been printed and made available to the public. These deal with Outpatient Services in Public Hospitals, Psychiatric Services in Public Hospitals, Services for the Deaf, the Medical Examination of Young Workers, Grading of Public Water Supplies, Occupational Deafness, the Employment of Dental Technicians, the Introduction of the Metric System in Pharmaceutical and Medical Practice, and the Training of Health Inspectors, the administration and servicing of Public Water Supplies, and the Health Responsibilities of Local Government.