The new rules for Medicare coverage proposed by the Health Care Financing Administration (HCFA) in the January 30 issue of the Federal Register deserve comment and support. Aside from making procedural changes in response to earlier public comment, HCFA proposes to include cost effectiveness as a criterion for the funding of a technology or procedure. This is a major step forward, but one that will not be without difficulties. Until now, Medicare coverage has required only that services be "reasonable and necessary"; cost has never been an explicit criterion. I think that the intelligent use of cost effectiveness as a . . .