The site at Soultz-sous-Forets (France) has been selected as the future European HDR research site (Garnish, J., Baria, R., Baumgartner, J., Gerard, A., 1994). GRC Trans. 18, 431-438; Baria, R., 1990. Proceedings of Camborne School of Mines. International HDR Conference, June 1989, p. 613. Robertson Scientific Publications, London). Since 1987, extensive testing of the underground has been carried out using a single well (GPK1), initially to a depth of 2000 m and then to a depth of around 3590 m. From 1995 onwards the testing of the underground has utilized two deep wells. The hydraulic tests carried out in 1993-1994 demonstrated the potential of the site as a future European Scientific Prototype. In particular, the tests showed that in the Rhine graben the fracture network in the basement is well-developed, with a degree of permeability. While some minor fluid movement occurs naturally, hydraulic simulation has been shown to increase substantially the overall transmissivity. The Soultz site has been used for testing a modified or alternative facet of the concept of HDR developed in recent years. The geological setting also offers other advantages in terms of relatively low stimulation pressures, a characteristic that may simplify the task of developing a promising circulation system. A second deep well (GPK2) was drilled late in 1994, with the aim of developing circulation between the two deep wells. In 1995, GPK2 was stimulated for the first time and a short circulation test was attempted between the two deep wells. During 1996, GPK2 was stimulated again using higher flow rates to improve the injectivity further. It is planned to install the necessary infrastructure to carry out, during 1997, a 4-month circulation test at around 25 kg/s, using a downhole pump to produce from GPK2 and reinjecting the produced fluid into CPI(I.