We have engaged in detailed multi-wavelength analysis of the March 26, 1991, solar flare in order to develop a method of diagnostics of the physical processes responsible for the efficient acceleration of charged particles to high energies and also for diagnostics of the photospheric response to the injection of the accelerated particles. Consideration of this particular flare is of special interest because to date it is the only flare in which the gamma-ray emission with energies of 20-1000 MeV was registered throughout the entire development of the event in the optical, radio and soft x-ray bands. individual registration by the GAMMA-1 telescope of the energy and precise time for each registered gamma-ray photon allowed the maximum detailed investigation of the energy spectrum and flux evolution during the flare.