Deposit interest rate deregulation and financial service innovation have led to dramatic changes in large banks' deposit composition. This paper presents a statistical cost analysis of changes in unit costs faced by banks under comprehensive financial deregulation. The results of this paper show that the unit cost of retail depositsdemand and passbook savings deposits-has increased relative to wholesale deposits-federal funds, certificates of deposit, and money market time deposits. We show, contrary to conventional wisdom, that changes in unit costs have been caused by processing costs rather than by interest expenses.Introduction and Overview Commercial banks in the last decade have experienced dramatic changes in deposit composition as a result of financial innovation and the phaseout of deposit interest rate ceilings. An important issue concerning these deregulative changes is their impact on banks' costs of providing financial services. The purpose of this paper is to present new empirical evidence concerning the effects of innovation and deregulation on the relative