they tell the drs. how much it will pay for any particular procedure. This the medicare "assignment". A doctor does not have to accept the medicare assignment in which case the patient would pay the balance. It is wise for a medicare beneficiary to assure him/herself that the dr. does accept the assignment amount. With the hospitalization part of Medicare there is a first day deductible, so supplemental coverage is advisable for those who might not be able to easily absorb that charge for the first day.