Three different types of biological experiments on samples of martian surface material ("soil") were conducted inside the Viking lander. In the carbon assimilation or pyrolytic release experiment, $^{14}$CO$_{2}$ and $^{14}$CO were exposed to soil in the presence of light. A small amount of gas was found to be converted into organic material. Heat treatment of a duplicate sample prevented such conversion. In the gas exchange experiment, soil was first humidified (exposed to water vapor) for 6 sols and then wet with a complex aqueous solution of metabolites. The gas above the soil was monitored by gas chromatography. A substantial amount of O$_{2}$ was detected in the first chromatogram taken 2.8 hours after humidification. Subsequent analyses revealed that significant increases in CO$_{2}$ and only small changes in N$_{2}$ had also occurred. In the labeled release experiment, soil was moistened with a solution containing several $^{14}$C-labeled organic compounds. A substantial evolution of radioactive gas was registered, but did not occur with a duplicate heat-treated sample. Alternative chemical and biological interpretations are possible for these preliminary data. The experiments are still in process, and these results so far do not allow a decision regarding the existence of life on the planet Mars.
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