A section of notes on geothermal exploration using the resistivity method precedes the main body of the paper. Field data from the Broadlands Area of New Zealand, Java, and the Imperial Valley, California are included. The reconnaissance resistivity survey recently completed in the East Mesa Area confirmed that a broad zone of low resistivities at depth extends through the area in a NNW direction. The interpretation of the resistivity data and the location of the resistivity lows at depth is much less definite in the Imperial Valley than it is in other areas of geothermal exploration. This is due to the extremely low background level of resistivities. The low resistivities in the Imperial Valley are due to the high porosity of the sediments and the high salinity of the solutions contained within the rock. The expected decrease in resistivity due to elevated temperature is much more difficult to detect in this environment. Edges of the zones of low resistivities have been delineated in almost all directions. (JGB)