Our limited understanding of the Martian environment has stimulated much speculation on the possible existence of a. Martin biota. This understanding is being steadily improved by ground-based observing techniques. Rapid advances have been made by the Mariner IV flyby and will be made by the Mariner 1969 flybys and the Mariner 1971 orbiters. In silly measurements, including some aimed at detecting manifestations of life, will be carried out on the Viking landers in 1973. We should then be in a position to diseuss more quantitatively than at present the various questions related to indigenous Martian life forms.