Medicare, authorized by title XVIII of the Social Security Act, is a health insurance program that helps almost all Americans age 65 or over and some disabled persons pay for needed health services. Medicare consists of two parts: Part A, Hospital Insurance for the Aged and Disabled, covers inpatient hospital services, skilled nursing facility services after a hospitalization, hospice services, and home health services. Part A is financed primarily by Social Security taxes on wages. To be eligible for part A, a person must (1) be 65 years of age or older and eligible for payments under Social Security's old age retirement and survivors program, (2) have received Social Security disability benefits for 24 months, or (3) suffer from end stage renal disease and be fully or currently insured under title II of the act. In fiscal year 1987, part A expenditures totaled about $50.8 billion. Part B, Supplementary Medical Insurance for the Aged and Disabled, is a voluntary program that covers physician services and a number of other health services, such as laboratory, outpatient hospital, and home health services. Part B is financed by enrollee premiums (currently set by law at an amount necessary to cover 25 percent of total costs) and federal general revenues. Any citizen, or legal alien who has resided in the United States for at least 5 years, age 65 or older is eligible for part B. In addition, disabled persons, and end stage renal disease patients eligible for part A are also eligible for part B. In fiscal year 1987, part B expenditures totaled about $30.8 billion.