Plant freezing and plant-growth inhibition are among the major problems in greenhouse cultivation in the central part of Argentina. The possibility of using a constant temperature underground geothermal water source, which flows naturally, has been studied as an economic option to solve these problems. A system of heating by means of geothermal energy, with energy-conservation measures, was designed and evaluated for typical production greenhouses in the southern part of Cordoba, Argentina. The results of tests carried out during 3 years are presented. These results are really promising, taking into account the high benefit/cost relation of the design and the availability of similar geothermal resources in many farms of this region.