Medical examinations and x-rays are conducted by qualified doctors and radiologists usually nominated by the department.

Outside Australia: Do not complete your health examination before you lodge your visa application - you will be advised when you need to do so.

Contact your nearest Australian diplomatic office for the health requirements, forms and available doctors.

In Australia: You may complete your health examination before lodging your application for a visa (and for some visas it is a formal requirement that you do).
Contact Health Services Australia (HSA), to arrange a medical examination, on 1300 361 046 or at www.healthoz.com.au. and to confirm whether digital photos will be taken.

Fees for medical examinations are set by HSA and you pay the fees directly to them.

The forms are available from the department's nearest regional office.

When you present yourself for your health examination, you should bring the following:

Form 26, Medical examination for an Australian visa, with a passport photograph attached. Onshore applicants should note that most HSA offices now take digital photos as part of the assessment process. Please contact HSA for confirmation,
Form 160, Radiological report on chest x-ray of an applicant for an Australian visa, with a passport photograph attached,
your passport for identification,
any prescription spectacles or contact lenses that you may wear, and
where you have a known medical condition, any existing specialist reports.
If you think or know that you are pregnant you must tell the person taking the x-ray. It is most likely that you will be asked to complete the x-ray examination after the birth.

If you are female, you should not undergo the medical examination during your menstrual period.
See:

Immigration Panel Doctors

Health Services Australia