[en] One of the main characteristics of the high-energy hadronic or nuclear collisions is the existence of large event-by-event fluctuations, manifested in several observed quantities. The effects of fluctuations in the initial conditions, by using the Interacting Gluon Model, modified by the inclusion also of the impact-parameter fluctuation is investigated. Some observables which follow directly from this model, such as the inelasticity and leading-particle distributions as well as the energy-dependence of the average inelasticity, exhibit a good agreement with all the existing data. The rapidity and pseudo-rapidity distributions calculated by applying the one-dimensional hydrodynamical model with fluctuating mass and momentum show a considerable deviation from those computed with the average initial conditions, using the same mechanism. To account for the semi-inclusive distributions and the forward-backward correlation, it is necessary to take into account also the multiplicity fluctuation, for fireballs of fixed masses. This has been done within the longitudinal phase-space model, with the energy and momentum distributions of the fireballs given by the IGM. (author)