This paper describes a detailed quantitative evaluation of the Residential Weatherization Pilot Program, operated by the Bonneville Power Administration from 1980 through 1982. The program provided free energy audits to more than 6000 electrically-heated homes and gave zero-interest loans to weatherize almost 4000 of these audited homes. The total cost of the program was almost $8 million. Using actual electricity consumption records for program participants and nonparticipants, we calculated the energy-saving effect of the pilot program in several ways and always reached the same conclusion. Households that received an audit and weatherization loan reduced their annual electricity consumption by about 3500 kWh relative to what they would have done without the program; this 3500 kWh is the saving that can be directly attributed to the program. Using a simple net present worth approach, the authors computed program benefits and costs for participating households, the BPA power system, and the Pacific Northwest region as a whole. Under a wide range of assumptions concerning discount rate, years until the weatherization loan is repaid, program energy saving, and BPA's marginal cost of power, the program is economically attractive from all three perspectives.