The recent detection of CH₄ in Mars atmosphere at an average ~10-20 ppb level [1, 2, 3 ,4] suggests that, either a subsurface hydrothermal activity, or some biogenic sources could still be active or have been active in a recent past. Assuming that CH₄ is produced at depth and transported up to the surface, it must necessarily experience a transition from gas to solid phase (CH₄ clathrate) in the zone from 3 km up to a few meters depth [5, 6]. Assuming that the lifetime of methane is of the order of 100 days [7], the present redox imbalance between the escape fluxes of H and O might be explained by the oxidation of CH₄ [8]. If so, the release rate of H₂, expected to be produced in the same time as CH₄ if the production mechanism is serpentinization, is not significant. The reason why no H₂ is released could be that CH₄ has been stored in subsurface clathrates before being released, whereas H₂ has been lost early after the CH₄-producing hydrothermal episode [8]. Another possible reason is that CH₄ is formed through homogeneous equilibration of carbon in deep hot fluids [9, 10]. A third reason could be that H₂ is consumed by bacterial activity in the crust. Interestingly, from a model of the hydrogen isotopic fractionation generated by the escape of serpentinization-derived hydrogen, only 20% of the presently released CH₄ could be due to serpentinization, suggesting other sources (like biology) [10]. The possibility of a biological origin for the Martian CH₄ will be discussed.