A novel method for detection of hydrogen by an electron beam in extremely thin samples is described. Elastically scattered electrons impinging with 20-30 keV on a thin formvar film were detected at a scattering angle near 45 degrees. In these large momentum transfer elastic collisions a clear separation of the signal of hydrogen and heavier elements was found. By changing the momentum transfer we can verify that the hydrogen signal is not due to inelastic energy loss contributions. The width of the hydrogen elastic peak is much larger than the elastic peaks due to heavy elements (carbon and oxygen). The ratio of the hydrogen elastic peak and the main elastic peak is smaller than expected by 30-50% depending on the energy of the impinging electron. This could be due to electronic excitations directly coupled to the elastic collision. The stability of the formvar film under electron radiation was studied. A reduction in thickness of the film with increasing fluence, as well as the preferential depletion of hydrogen, was found. Possible improvements of the experimental configuration for this type of experiments are discussed.