  In this paper we reconsider the constraints which are imposed by relativistic
requirements to any model of dynamical reduction. We review the debate on the
subject and we call attention on the fundamental contributions by Aharonov and
Albert. Having done this we present a new formulation, which is much simpler
and more apt for our analysis, of the proposal put forward by these authors to
perform measurements of nonlocal observables by means of local interactions and
detections. We take into account recently proposed relativistic models of
dynamical reduction and we show that, in spite of some mathematical
difficulties related to the appearence of divergences, they represent a
perfectly appropriate conceptual framework which meets all necessary
requirements for a relativistic account of wave packet reduction. Subtle
questions like the appropriate way to deal with counterfactual reasoning in a
relativistic and nonlocal context are also analyzed in detail.
