The possibility of producing the base load of both electricity and district heat for the Helsinki Metropolitan Area (HMA) utilizing nuclear energy has been investigated since 1968. At every stage of the study, it has been concluded that district heating utilizing nuclear power in combined electricity and heat production is the most economic way of heating the main part of the HMA. The studies have dealt with the economy of energy production and heat transmission as well as nuclear safety. According to the latest results, the optimum of the heat output of a 1000-MW(electric) unit is ∼800 MW if the plant is situated 50 km away from the heat load center. For further studies and realization of the plans, the cities of the HMA and the state-owned power company, the Imatra Power Company, have formed a common company for the nuclear power plant project.