Microbiological studies of the Antarctic dry valleys are reviewed from the standpoint of their application to Martian exploration. The mean low temperature, the difference in temperature between surface and atmosphere, and aridity are common to both the dry valleys and to Mars. Experiments have shown that shortage of water limits the valley life which is almost entirely microbial. It is suggested that the Mars environment is decidedly more hostile than that of the Antarctic and the fear that terrestrial microorganisms carried to Mars could multiply and contaminate the plantet is unfounded. If Martian life exists, it must have evolved special means for obtaining and retaining water, assuming that water is the Martian biological solvent. The findings show that even under severe selective pressure, microbial life in the Antarctic has been unable to discover a comparable mechanism. However, a conclusion that life on Mars is an impossibility is not justified.