Review: Construction of a borehole heat store in Lulea, Sweden, began in August 1982. This seasonal heat store consists of 100 000 m s of granite. The rock volume is perforated by 120 boreholes to a depth of 65 m. The heat store has been in operation since 1983. The research work, funded by the Swedish Council for Building Research and conducted at the Lulea University of Technology, will continue until 1988. This research report describes the design and construction of the Lulea store.