The detection and identification of organic compounds at the surface of Mars is important to the question of the existence of living systems or their eventual evolution. There are two general approaches to this problem: either an instrument specifically designed to detect a certain compound or group of compounds known to be a prerequisite or product at least of terrestrial living systems, or a nonspecific survey instrument which would be capable of detecting whatever compounds are there. The latter does not require any terrestrial model for Martian organic chemistry and is thus preferred. A mass spectrometer is the most sensitive and nonspecific instrument for this purpose. Combination with a gas Chromatograph increases the capability to handle complex mixtures and to give interpretable mass spectra of the individual components.