With the recent advent of table-top terawatt Ti:Sa laser amplifier systems, laser plasma interactions provide high-energy, femtosecond electron bunches, which might conjecture direct observation of radiation events in media of biological interest. We report on the first femtolysis studies using such laser produced relativistic electron pulses in the 2.5-15 MeV range. A real-time observation of elementary radical events is performed on water molecules and media containing an important disulfide biomolecule. The primary yield of a reducing radical produced in clusters of excitation-ionisation events (spurs) has been determined at t~3.5 10^-12 s. These data provide important information about the initial energy loss and spatial distribution of early radical events. Femtolysis studies devoted to a disulfide biomolecule is noteworthy as it is the first time that a primary ionisation event can be controlled by an ultrafast radical anion formation in the prethermal regime. This innovating domain foreshadows the development of new applications in radiobiology (microdosimetry at the nanometric scale). In the near future, electron femtolysis studies would clearly enhance the understanding of radiation-induced damages in biological confined spaces (aqueous groove of DNA and protein pockets).